







27000001 
20171009 

From Tulashiram: If aŚ b =27000001, then what is the value of a & b ? Answered by Penny Nom. 





The units digit of a prime 
20150108 

From Patricia: Every prime number greater than 10 has a digit in the ones place that is included in which set of numbers below 1 3 7 9 or 1 3 7 or 0 2 4 5 6 8 or 1 3 5 9 Answered by Walter Whiteley. 





One factor array 
20110916 

From Hana: hi my brother a 5th grade have a question. this is what it say "i have only one factor array, and i am between two numbers 12 and 16. what number am i?" Answered by Penny Nom. 





What is the largest prime number? 
20101120 

From vadali: what is the largest prime number? Answered by Penny Nom. 





The cardinality of the prime numbers 
20091107 

From Justin: Hello there, I was just wondering since the number of primes is infinite,
are they equal to infinity or Alephnull?
Justin Answered by Robert Dawson and Victoria West. 





Primes 
20090625 

From Chinonyerem: If p = 2^k  1 is prime, show that k is an odd integer, except when k = 2.
[ Hint: 3/4^n  1 for all n >= 1.] Answered by Robert Dawson and Penny Nom. 





A positive integer with 2007 digits 
20080206 

From Tom: Prove that there's a unique positive integer of 2007 digits lenght, divisible by 2^2007, and made up solely by the digits 2 and 5. Answered by Penny Nom. 





I am a prime number 
20071031 

From sherry: I am a prime number. I can not be shared fairly except by one group. My array can only be one row.
array can only be one row. Can you please explain this out to me so I can help my child with it.
Thanks Answered by Penny Nom. 





Prime numbers 
20070116 

From A student: are the product of two prime numbers always prime? Answered by Penny Nom. 





The sum of prime numbers 
20061128 

From Rambabu: I would like to know the sum of prime numbers below some X say 10000. Provide me with easy way to get this done Answered by Penny Nom. 





given that p is a prime and pa^n, prove that p^na^n 
20060324 

From Janna: given that p is a prime and pa^{n}, prove that p^{n}a^{n} Answered by Stephen La Rocque. 





Write the array for 3 
20060129 

From Jamie: My son is a 5th grader and came home with a math question that I can't answer. The question stated  "Write the array for 3" I don't understand how this can be done with just one number. Answered by Penny Nom. 





GCF, LCM, primes and the ladder method 
20060107 

From Linda: How would I teach both finding the GCF and LCM with prime factors...I recall the ladder method vaguely.??? Answered by Penny Nom. 





A two digit prime 
20050912 

From A student: The units digit of a twodigit prime number is not greater than the tens digit by 3.If the positions of the two digits are interchanged, then the new number formed is greater than the original number by more than 18. Find the value of the original prime number. Answered by Penny Nom. 





Primes 
20050604 

From Fede: Prove that there is not a number prime p, for which the numbers p+5 and p+10 are prime too. Answered by Penny Nom. 





The numbers p and 8p^2 +1 are prime. 
20050530 

From Antonio: The numbers p and 8p^{2} +1 are prime. Prove that the number 8p^{2}+2p+1 is also a prime number. Answered by Claude Tardif and Penny Nom. 





Prime numbers 
20050411 

From Jesule: Given that p, p+10 and p+14 are prime numbers, find p. Answered by Claude Tardif and Chris Fisher. 





Divisors of 2n+1 and 3n+9 
20040602 

From Chris: Amy selected a positive integer N and wrote numbers 2xN+1 and 3xN+9 on a whiteboard. Boris looked at the two numbers on the whiteboard and wrote in his notebook a positive integer that divides each of them. Find all possible numbers that Boris could have written in his notebook. Answered by Chris Fisher and Penny Nom. 





Pairs of prime numbers 
20031013 

From Nikolas: Use pairs of prime numbers to find all the numbers less than 50 that have only two prime factors. Make an organized list. Answered by Penny Nom. 





Primes 
20030923 

From Julie:
#1. Suppose you are given a number (n) and told that 1 and the number (n) divide into (n). Does that mean (n) is prime? #2. Suppose that p is a prime number greater than or equal to 3. Show that p+1 cannot be a prime number. Answered by Penny Nom. 





The Sieve of Eratosthenes 
20030918 

From Lynn: My daughter has been asked to find all the prime numbers by using the Sieve of Eratosthenes. I have no understanding what this means. Answered by Penny Nom and Claude Tardif. 





Why is 5 divided by 1/7 greater than 5 divided by 2/3? 
20021119 

From Elizabeth:
 Without performing the division, explain why 5 divided by 1/7 is a number greater than 5 divided by 2/3.
 Is the least common multiple of two prime numbers always their product? Why or why not?
Answered by Diane Hanson and Penny Nom. 





Prime numbers 
20021108 

From Lonna: Is 2 a prime number or not?? Why is 1 not considered a prime number? Answered by Penny Nom. 





Neither prime nor composite 
20010508 

From Marc: what 2 numbers are neither prime nor combitative? Answered by Penny Nom. 





Tshirts 
19990404 

From Valerie: At a discount Tshirt shop the manager marked a special batch of Tshirts that originally sold for $2.00. When all the shirts sold the shop had collected $603.77. How many shirts did they sell and what was the price per shirt? Answered by Jack LeSage and Penny Nom. 





Divisors of 6n 
19980126 

From James: If n is a positive integer such that 2n has 28 positive divisors and 3n has 30 positive divisors, then how many positive divisors does 6n have? (a) 32 (b) 34 (c) 35 (d) 36 (e) 38 Answered by Penny Nom and Haragauri Gupta. 





Prime Numbers 
19970904 

From Jack Bedard: Hi. I have a real stupid question What are prime numbers? My name is Jack Bedard and I am in grade 5. Answered by Penny Nom. 





How do you find out if a number is a composite or prime? 
19960916 

From Trish Feenstra: Hi my name is Trish Feenstra. In grade 8. How do you find out if a number is a composite or prime if it is big like 37 529? Reply soon got a test on Friday the 13th Answered by Denis Hanson. 





Prime numbers 
19960222 

From Charles Hewitt: I would apprecaite it if you could share with me any algorithm to determine whether a number is prime. Answered by Penny Nom. 





2^(2^1954) estil premier? 
20051004 

From Un eleve: 2^{(21945)}+1 estil premier? Answered by Claude Tardif. 

