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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, 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.
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
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Sep 30 2009
EXTENSIONS
Extension and program from Charles R Greathouse IV, Oct 12 2009
STATUS
approved