A050108 a(n) = floor(a(n-1)/4) if this is positive and not yet in the sequence, otherwise a(n) = 5*a(n-1).

1, 5, 25, 6, 30, 7, 35, 8, 2, 10, 50, 12, 3, 15, 75, 18, 4, 20, 100, 500, 125, 31, 155, 38, 9, 45, 11, 55, 13, 65, 16, 80, 400, 2000, 10000, 2500, 625, 156, 39, 195, 48, 240, 60, 300, 1500, 375, 93, 23, 115, 28, 140, 700, 175, 43, 215

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A050000 and references therein.

Programs

Mathematica

Rest@Nest[Append[#, If[FreeQ[#, r = Quotient[#[[-1]], 4]], r, 5 #[[-1]]]] &, {0, 1}, 55] (* Ivan Neretin, Jul 31 2016 *)

PARI

first(n)=my(v=vector(n),t); v[1]=1; for(i=2,n, t=v[i-1]\4; if(t<2, v[i]=5*v[i-1]; next); for(j=1,i-1, if(v[j]==t, v[i]=5*v[i-1]; next(2))); v[i]=t); v \\ Charles R Greathouse IV, Jul 31 2016