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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, 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 (list; graph; refs; listen; history; text; internal format)
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: A000991 A095093 A280473 * A062483 A174013 A081056

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

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Last modified April 21 20:03 EDT 2019. Contains 322328 sequences. (Running on oeis4.)