A178174 a(1)=a(2)=a(3)=a(4)=1; thereafter a(n) = gpf(a(n-1)+a(n-2)+a(n-3)+a(n-4)), where gpf is the greatest prime factor.

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

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, 358-362.

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