

A074871


Start with n and repeatedly apply the map k > T(k) = A053837(k) + A171765(k); a(n) is the number of steps (at least one) until a prime is reached, or 0 if no prime is ever reached.


2



0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 2, 1, 0, 1, 1, 0, 1, 0, 1, 2, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 2, 2, 1, 0, 0, 0, 1, 0, 1, 0, 1, 2, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 0, 1, 2, 2, 0, 1, 3, 2, 2, 1, 1, 2, 1, 2, 1, 1, 2, 1, 1, 2, 0, 1, 2, 2, 2, 1, 2, 1, 2, 1, 0, 0, 1, 1, 2, 3, 1, 2, 1, 1, 0, 1, 1, 0, 1, 0
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OFFSET

1,17


COMMENTS

The first occurrence of k beginning with 0: 1, 2, 17, 59, 337, 779, 16999, 6888888, ..., .  Robert G. Wilson v, Oct 20 2010


LINKS

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


EXAMPLE

T(2)=2. So in one step we reach a prime.
T(3)=3 and then in one step again we reach a prime.
T(4)=4 and we will never reach a prime.
T(11)=1+2=3 and again in one step we reach a prime.
T(17)=7+8=15 > T(15)=5+6=11 and then in two steps we reach a prime.
T(13)=3+4=7 and then 1 step......
T(14)=4+5=9 > T(9)=9 > T(9)=9........ and we will never reach a prime.


MATHEMATICA

g[n_] := Block[{id = IntegerDigits@ n}, Mod[ Plus @@ id, 10] + If[n < 10, 0, Times @@ id]]; f[n_] := Block[{lst = Rest@ NestWhileList[g, n, UnsameQ, All]}, lsp = PrimeQ@ lst; If[ Last@ Union@ lsp == False, 0, Position[lsp, True, 1, 1][[1, 1]]]]; Array[f, 105] (* Robert G. Wilson v, Oct 20 2010 *)


CROSSREFS

Cf. A053837, A171765. See A171772 for another version.
Sequence in context: A141702 A259896 A113313 * A182641 A319020 A099200
Adjacent sequences: A074868 A074869 A074870 * A074872 A074873 A074874


KEYWORD

easy,nonn,base


AUTHOR

Felice Russo, Sep 12 2002, Oct 11 2010


EXTENSIONS

Edited by N. J. A. Sloane, Oct 12 2010
More terms from Robert G. Wilson v, Oct 20 2010


STATUS

approved



