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A128216 a(1)=a(2)=1. a(n+1) = a(n) + a(smallest prime dividing n). 2
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 (list; graph; refs; listen; history; text; internal format)
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: A057762 A109511 A018339 * A299322 A080735 A091856

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

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Last modified August 20 06:54 EDT 2018. Contains 313909 sequences. (Running on oeis4.)