A165929 a(1) = 1; for n > 1, a(n) = sigma(sum of the previous terms) where sigma(k) = sum of the divisors of k.

1, 1, 3, 6, 12, 24, 48, 120, 264, 480, 1104, 2064, 4128, 10752, 19320, 38328, 91992, 170016, 369600, 745560, 1854720, 3845760, 7765296, 14990520, 29910120, 59856720, 119710416, 298755600, 667297320, 1446528360, 4011171840

Offset

1,3

Comments

a(1) = 1; for n > 1, a(n) = sigma(Sum_{i=1..n-1} a(i)) = A000203(Sum_{i=1..n-1} a(i)).

a(n) = inverse of partial sums of A081973(n), i.e., a(1) = A081973(1); for n > 1, a(n) = A081973(n) - A081973(n-1), i.e., first differences of A081973.

Links

Table of n, a(n) for n=1..31.

Example

a(4) = sigma(a(1) + a(2) + a(3)) = sigma(1+1+3) = sigma(5) = 6.

Mathematica

Module[{lst={1}}, Do[AppendTo[lst, DivisorSigma[1, Total[lst]]], {40}]; lst] (* Harvey P. Dale, Sep 29 2012 *)

Prog

(PARI) print1(1); s=1; for(i=1, 100, k=sigma(s); print1(", "k); s+=k)

Crossrefs

Sequence in context: A049942 A200463 A099844 * A084717 A102254 A278666

Adjacent sequences: A165926 A165927 A165928 * A165930 A165931 A165932

Keyword

nonn

Author

Jaroslav Krizek, Sep 30 2009

Extensions

Extension and program from Charles R Greathouse IV, Oct 12 2009

Status

approved