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A108672 a(n) = Sum{k=1 to n} sigma_{n-k+1}(k), where sigma_m(k) = sum{j|k} j^m. 1
1, 4, 10, 27, 73, 227, 767, 2860, 11569, 50363, 234155, 1156037, 6031747, 33130183, 190929773, 1151198266, 7243777228, 47462906925, 323188163747, 2282922216815, 16701529748617, 126359471558611, 987316752551411, 7957198067362137 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..24.

EXAMPLE

a(5) = 1^5 + (1^4 +2^4) + (1^3 +3^3) + (1^2 +2^2 +4^2) + (1^1 +5^1) = 1 + 17 + 28 + 21 + 6 = 73.

MAPLE

with(numtheory): s:=proc(n, k) local div: div:=divisors(n): sum(div[j]^k, j=1..tau(n)) end: a:=n->sum(s(i, n-i+1), i=1..n): seq(a(n), n=1..25); # Emeric Deutsch, Jul 13 2005

PROG

(PARI) a(n) = sum(k=1, n, sigma(k, n-k+1)); \\ Michel Marcus, Aug 16 2019

CROSSREFS

Cf. A108699 (with product).

Sequence in context: A077923 A183325 A052982 * A000495 A027067 A050262

Adjacent sequences:  A108669 A108670 A108671 * A108673 A108674 A108675

KEYWORD

nonn

AUTHOR

Leroy Quet, Jul 07 2005

EXTENSIONS

More terms from Emeric Deutsch, Jul 13 2005

STATUS

approved

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Last modified July 13 22:21 EDT 2020. Contains 335716 sequences. (Running on oeis4.)