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A007437 Inverse Moebius transform of triangular numbers.
(Formerly M3309)
18
1, 4, 7, 14, 16, 31, 29, 50, 52, 74, 67, 119, 92, 137, 142, 186, 154, 247, 191, 294, 266, 323, 277, 455, 341, 446, 430, 553, 436, 686, 497, 714, 634, 752, 674, 1001, 704, 935, 878, 1150, 862, 1298, 947, 1323, 1222, 1361, 1129, 1767, 1254, 1674, 1486, 1834 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

M. Bernstein and N. J. A. Sloane, Some canonical sequences of integers, Linear Alg. Applications, 226-228 (1995), 57-72; erratum 320 (2000), 210. [Link to arXiv version]

M. Bernstein and N. J. A. Sloane, Some canonical sequences of integers, Linear Alg. Applications, 226-228 (1995), 57-72; erratum 320 (2000), 210. [Link to Lin. Alg. Applic. version together with omitted figures]

N. J. A. Sloane, Transforms

FORMULA

Coefficients in expansion of Sum_{n >= 1} x^n/(1-x^n)^3.

G.f.: sum(n>=1, (n*(n+1)/2) * x^n/(1-x^n) ). - Joerg Arndt, Jan 30 2011

a(n)=sum(d|n, d*(d+1)/2)= (1/2) *(sigma(n)+sigma_2(n))= (1/2) *(A000203(n)+A001157(n)). - Benoit Cloitre, Apr 08 2002

Row sums of triangles A134544 and A134545. - Gary W. Adamson, Oct 31 2007

Row sums of triangle A134839 - Gary W. Adamson, Nov 12 2007

Dirichlet g.f. zeta(s)*(zeta(s-1)+zeta(s-2))/2. [From Franklin T. Adams-Watters, Nov 05 2009]

L.g.f.: -log(Product_{k>=1} (1 - x^k)^((k+1)/2)) = Sum_{n>=1} a(n)*x^n/n. - Ilya Gutkovskiy, Mar 12 2018

Sum_{k=1..n} a(k) ~ Zeta(3) * n^3 / 6. - Vaclav Kotesovec, Nov 06 2018

MAPLE

with (numtheory):

a:= proc(n) option remember;

      add( d*(d+1)/2 , d=divisors(n))

    end:

seq (a(n), n=1..60);  # Alois P. Heinz, Feb 09 2011

MATHEMATICA

a[n_] := (DivisorSigma[1, n] + DivisorSigma[2, n])/2; Table[a[n], {n, 1, 60}] (* Jean-Fran├žois Alcover, Mar 10 2014, after Benoit Cloitre *)

PROG

(PARI) a(n)=if(n<1, 1, sumdiv(n, d, (d^2+d))/2); /* Joerg Arndt, Aug 14 2012 */

CROSSREFS

Cf. A134544, A134545.

Cf. A134839, A301873, A301874.

Sequence in context: A310897 A310898 A310899 * A310900 A310901 A310902

Adjacent sequences:  A007434 A007435 A007436 * A007438 A007439 A007440

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Christian G. Bower.

STATUS

approved

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Last modified February 21 10:49 EST 2019. Contains 320372 sequences. (Running on oeis4.)