college
posted by dayo on .
what's the relation between these numbers 1,2,4,9,16,25,36,...

Think "squares."
http://www.mathsisfun.com/squareroot.html 
The subject is maths.
These are positive integers n such that the sum of the divisors of n, excluding 1, is a multiple of the number of divisors of n.
so the next numbers in the sequence are
64, 81, 100, 121, 289,
As examples
The 9 divisors of 36 are {1,2,3,4,6,9,12,18,36}, giving sum (1+2+3=4+6+9+12+18+36)1=90 which is a multiple of 9. Thus 36 is a term of the sequence.
The 3 divisors of 25 are
{1,5,25} giving a sum (1+5+25)1=30 which is a multiple of 3. Thus 25 is a term of the sequence. 
it's not square cuz i want the relation btw these numbers 1,2,4,9,16,25,36,.. NOT btw these numbers 1,4,9,16,25,...

Agreed it is not squares. It is the sequence as I described above.