OFFSET
0,2
COMMENTS
Only squares have an odd number of divisors.
FORMULA
a(n) <= 2^n, where the equality holds if and only if n=0 or 2n+1 is prime. - Jianing Song, Aug 30 2021
EXAMPLE
a(4)=6 because it is the smallest number followed by 10,14,15,16,21,22,... whose squares have 2*4 + 1, i.e., 9 divisors.
PROG
(PARI) a(n) = {k = 1; while (numdiv(k^2) != (2*n+1), k++); return (k); } \\ Michel Marcus, Jul 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Lekraj Beedassy, May 31 2002
EXTENSIONS
More terms from Vladeta Jovovic, Jun 05 2002
a(0) prepended by Jianing Song, Aug 30 2021
STATUS
approved