A139423 - OEIS

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, 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

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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 * A363459 A026053 A276031

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