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A139423 a(1)=1, a(2)=2. 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, 2, 5, 9, 14, 21, 29, 35, 41, 47, 51, 57, 65, 73, 79, 83, 87, 93, 101, 107, 111, 117, 127, 135, 145, 157, 163, 167, 171, 179, 187, 193, 199, 203, 209, 217, 225, 238, 255, 271, 281, 285, 295, 307, 313, 317, 321, 327, 335, 343 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

MAPLE

with(numtheory): a[1]:=1: a[2]:=2: 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 30 2008

MATHEMATICA

Join[{a = 1, b = 2}, Table[c = b + Total[DivisorSigma[0, {a, b}]]; a = b; b = c; c, {n, 48}]] (* Jayanta Basu, Jun 06 2013 *)

CROSSREFS

Cf. A139422, A064491.

Sequence in context: A191170 A191123 A152888 * A026053 A276031 A011905

Adjacent sequences:  A139420 A139421 A139422 * A139424 A139425 A139426

KEYWORD

nonn

AUTHOR

Leroy Quet, Apr 21 2008

EXTENSIONS

More terms from Emeric Deutsch, Apr 30 2008

STATUS

approved

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Last modified June 1 20:49 EDT 2020. Contains 334765 sequences. (Running on oeis4.)