A128216 a(1)=a(2)=1. a(n+1) = a(n) + a(smallest prime dividing n).

1, 1, 2, 4, 5, 10, 11, 22, 23, 25, 26, 52, 53, 106, 107, 109, 110, 220, 221, 442, 443, 445, 446, 892, 893, 898, 899, 901, 902, 1804, 1805, 3610, 3611, 3613, 3614, 3619, 3620, 7240, 7241, 7243, 7244, 14488, 14489, 28978, 28979, 28981, 28982, 57964, 57965

Offset

1,3

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Example

The smallest prime dividing 12 is 2. So a(13) = a(12) + a(2) = 52 + 1 = 53.

Maple

with(numtheory): a[1]:=1:a[2]:=1:for n from 2 to 55 do a[n+1]:=a[n]+a[factorset(n)[1]] od: seq(a[n], n=1..55); # Emeric Deutsch, Mar 07 2007

Mathematica

a128216[1] = 1; a128216[2] = 1;
a128216[n_] := a128216[n] = a128216[n-1] + a128216[First[First[FactorInteger[n-1]]]];
Array[a128216, 49] (* data *) (* Hartmut F. W. Hoft, Mar 08 2017 *)

Crossrefs

Cf. A128215, A020639.

Sequence in context: A109511 A018339 A328009 * A299322 A365501 A080735

Adjacent sequences: A128213 A128214 A128215 * A128217 A128218 A128219

Keyword

nonn

Author

Leroy Quet, Feb 19 2007

Extensions

More terms from Emeric Deutsch, Mar 07 2007

Status

approved