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A160689 a(1)=1. a(n) = the smallest positive integer such that d(a(n)) = d(Sum_{k=1..n} a(k)), where d(m) = the number of divisors of m. 5
1, 2, 2, 2, 8, 2, 2, 8, 2, 2, 8, 2, 2, 8, 2, 21, 5, 6, 6, 15, 3, 6, 8, 6, 2, 10, 12, 6, 12, 2, 10, 22, 8, 6, 34, 6, 6, 22, 8, 6, 8, 2, 2, 6, 8, 8, 2, 6, 15, 31, 6, 2, 6, 8, 6, 2, 2, 6, 10, 2, 6, 6, 15, 13, 6, 2, 6, 8, 2, 8, 6, 10, 6, 10, 8, 8, 6, 8, 6, 10, 8, 2, 2, 10, 2, 10, 6, 2, 38, 10, 6, 10, 8, 10, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Sum_{k=1..n} a(k) = A160690(n).
d(a(n)) = d(A160690(n)) = A160691(n).
LINKS
MATHEMATICA
a[1] = 1; a[n_] := a[n] = (s = Sum[a[k], {k, n-1}]; For[m = 1, DivisorSigma[0, m] != DivisorSigma[0, s + m], m++]; m); Table[a[n], {n, 95}] (* Farideh Firoozbakht, May 28 2009 *)
PROG
(PARI) lista(nn) = {k = 1; print1(k, ", "); s = k; for (n=2, nn, k = 1; while(numdiv(k) != numdiv(k+s), k++); print1(k, ", "); s += k; ); } \\ Michel Marcus, Sep 04 2017
CROSSREFS
Sequence in context: A087421 A309574 A132697 * A179976 A137508 A055921
KEYWORD
nonn
AUTHOR
Leroy Quet, May 24 2009
EXTENSIONS
More terms from Farideh Firoozbakht, May 28 2009
STATUS
approved

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Last modified March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)