A139422 a(1)=a(2)=1. For n >= 3, a(n) = a(n-1) + d(a(n-1)) + d(a(n-2)), where d(m) is the number of positive divisors of m.

1, 1, 3, 6, 12, 22, 32, 42, 56, 72, 92, 110, 124, 138, 152, 168, 192, 222, 244, 258, 272, 290, 308, 328, 348, 368, 390, 416, 444, 468, 498, 524, 538, 548, 558, 576, 609, 638, 654, 670, 686, 702, 726, 754, 774, 794, 810, 834, 862, 874

Offset

1,3

Links

Table of n, a(n) for n=1..50.

Maple

with(numtheory): a[1]:=1: a[2]:=1: for n from 3 to 50 do a[n]:=a[n-1]+tau(a[n-1])+tau(a[n-2]) end do: seq(a[n], n=1..50); # Emeric Deutsch, Apr 26 2008

Mathematica

Join[{a = 1, b = 1}, Table[c = b + Total[DivisorSigma[0, {a, b}]]; a = b; b = c; c, {n, 48}]] (* Jayanta Basu, Jun 06 2013 *)

Crossrefs

Cf. A139423, A064491.

Sequence in context: A095093 A280473 A333820 * A062483 A174013 A309266

Adjacent sequences: A139419 A139420 A139421 * A139423 A139424 A139425

Keyword

nonn

Author

Leroy Quet, Apr 21 2008

Extensions

More terms from Emeric Deutsch, Apr 26 2008

Status

approved