OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = sigma(n(3n-1)/2), where sigma is the sum of divisors function. - Emeric Deutsch, Apr 15 2006
Sum_{k=1..n} a(k) ~ (9/10) * n^3. - Amiram Eldar, Dec 14 2024
EXAMPLE
a(5) = 48 because the divisors of 5*(3*5-1)/2 = 35 are 1, 5, 7 and 35, having sum 48.
MAPLE
with(numtheory): seq(sigma(n*(3*n-1)/2), n=1..46); # Emeric Deutsch, Apr 15 2006
MATHEMATICA
Table[DivisorSigma[1, (n(3n-1))/2], {n, 50}] (* Harvey P. Dale, Jul 05 2015 *)
PROG
(PARI) a(n) = sigma(n*(3*n-1)/2); \\ Amiram Eldar, Dec 14 2024
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Apr 04 2006
EXTENSIONS
a(0) removed by Amiram Eldar, Aug 17 2019
STATUS
approved