A117948 Sum of the divisors of pentagonal numbers.

1, 6, 28, 36, 48, 72, 144, 168, 182, 180, 372, 576, 280, 336, 864, 720, 558, 702, 1120, 1080, 1024, 1008, 1296, 2016, 1178, 1344, 3600, 2016, 1320, 2160, 2304, 3720, 2736, 1836, 4704, 4212, 2736, 2280, 5040, 6048, 2604, 4992, 5588, 4752, 5304, 3312

Offset

1,2

Comments

See also: A000326 Pentagonal numbers: n(3n-1)/2. A000203 sigma(n) = sum of divisors of n. Also called sigma_1(n). A074285 Sum of the divisors of n-th triangular number. A117949 Indices of pentagonal numbers whose sum of divisors is square.

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

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 *)

Crossrefs

Cf. A000203, A000326, A074285, A117949.

Sequence in context: A083865 A185351 A272971 * A252234 A334405 A242344

Adjacent sequences: A117945 A117946 A117947 * A117949 A117950 A117951

Keyword

easy,nonn

Author

Jonathan Vos Post, Apr 04 2006

Extensions

a(0) removed by Amiram Eldar, Aug 17 2019

Status

approved