

A178174


a(1)=a(2)=a(3)=a(4)=1; thereafter a(n) = gpf(a(n1)+a(n2)+a(n3)+a(n4)), where gpf is the greatest prime factor.


2



1, 1, 1, 1, 2, 5, 3, 11, 7, 13, 17, 3, 5, 19, 11, 19, 3, 13, 23, 29, 17, 41, 11, 7, 19, 13, 5, 11, 3, 2, 7, 23, 7, 13, 5, 3, 7, 7, 11, 7, 2, 3, 23, 7, 7, 5, 7, 13, 2, 3, 5, 23, 11, 7, 23, 2, 43, 5, 73, 41, 3, 61, 89, 97, 5, 7, 11, 5, 7, 5, 7, 3, 11, 13, 17, 11, 13, 3, 11, 19, 23, 7, 5, 3, 19, 17, 11, 5, 13, 23, 13, 3, 13, 13, 7, 3, 3, 13, 13, 2, 31, 59, 7, 11, 3, 5, 13, 2, 23, 43, 3, 71, 7, 31
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OFFSET

1,5


COMMENTS

After 133 steps, enters a cycle of length 14.


LINKS

Table of n, a(n) for n=1..114.
Greg Back and Mihai Caragiu, The Greatest Prime Factor and Recurrent Sequences, Fibonacci Quart. 48 (2010), no. 4, 358362.


MATHEMATICA

nxt[{a_, b_, c_, d_}]:={b, c, d, FactorInteger[a+b+c+d][[1, 1]]}; Transpose[ NestList[ nxt, {1, 1, 1, 1}, 120]][[1]] (* Harvey P. Dale, Sep 24 2013 *)


CROSSREFS

Cf. A006530, A175723, A177904.
Sequence in context: A110315 A275677 A221183 * A094744 A229608 A185061
Adjacent sequences: A178171 A178172 A178173 * A178175 A178176 A178177


KEYWORD

nonn,easy


AUTHOR

N. J. A. Sloane, Dec 18 2010


STATUS

approved



