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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 (list; graph; refs; listen; history; text; internal format)
 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 EXAMPLE For n=4 the 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

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Last modified August 23 22:20 EDT 2019. Contains 326254 sequences. (Running on oeis4.)