A145280 - OEIS

A145280

Fecundity of n-th prime.

9, 9, 1, 7, 8, 7, 6, 3, 4, 3, 3, 3, 4, 2, 2, 8, 1, 2, 1, 4, 2, 2, 1, 3, 1, 0, 0, 0, 0, 7, 5, 3, 3, 2, 8, 6, 2, 6, 1, 2, 4, 5, 1, 1, 1, 1, 5, 5, 2, 4, 5, 9, 9, 4, 7, 7, 9, 5, 2, 6, 2, 8, 0, 11, 3, 2, 1, 1, 7, 4, 8, 7, 2, 2, 2, 3, 1, 22, 0, 0, 3, 2, 6, 4, 3, 5, 3, 3, 5, 2, 4, 5, 4, 4, 4, 0, 0, 5, 4, 6, 2, 3, 7, 2, 1

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..105.

FORMULA

a(n) = A070562(prime(n)). - Michel Marcus, Aug 01 2015

EXAMPLE

7 -> 7+7=14 -> 14+1*4=18 -> 18+1*8=26 -> 26+2*6=38 -> 38+3*8=62 -> 62+6*2=74 -> 74+7*4=102 -> 7 steps to reach a zero digit.

MAPLE

P:=proc(i) local a, b, c, ok, k, w, n; for n from 1 by 1 to i do a:=ithprime(n); b:=1; c:=0; ok:=1; while ok=1 do k:=a; w:=1; while k>0 do w:=w*(k-(trunc(k/10)*10)); k:=trunc(k/10); od; if w=0 then ok:=0; else c:=c+1; a:=a+w; fi; od; print(c); od; end: P(100);

MATHEMATICA

f[n_] := Length@ FixedPointList[ # + Times @@ IntegerDigits@# &, n] - 2; Array[f@Prime@# &, 105] (* Robert G. Wilson v, Jun 27 2010 *)

CROSSREFS

Cf. A070562, A145279.

Sequence in context: A346439 A266555 A343367 * A144667 A118428 A166925

Adjacent sequences: A145277 A145278 A145279 * A145281 A145282 A145283

KEYWORD

easy,nonn,base

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, Oct 06 2008

STATUS

approved