OFFSET
0,5
COMMENTS
All bits of n in positions not divisible by a(n) are zero. Hence n in binary contains blocks of a(n)-1 "diluting" 0's (for n>1). Also for n>1, a(2^n) = a(2^n + 1) = n. For i,j odd, a(ij) = GCD(a(i),a(j)).
LINKS
Peter Kagey, Table of n, a(n) for n = 0..10000
EXAMPLE
577 = 2^0 + 2^6 + 2^9, GCD(0,6,9) = 3 = a(577).
MATHEMATICA
A064894[n_] := Apply[GCD, Flatten[Position[Reverse[IntegerDigits[n, 2]], 1]] - 1];
Array[A064894, 100, 0] (* Paolo Xausa, Feb 13 2024 *)
PROG
(PARI) a(n) = if (n==0, 0, my(ve = select(x->x==1, Vecrev(binary(n)), 1)); gcd(vector(#ve, k, ve[k]-1))); \\ Michel Marcus, Apr 12 2016
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Marc LeBrun, Oct 11 2001
STATUS
approved