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

Author

Leroy Quet, Apr 21 2008

Keywords

• nonn

Crossrefs

Cf. A139423, A064491.

Programs

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 *)

Extensions

More terms from Emeric Deutsch, Apr 26 2008