A127203 a(n) = gcd(A127202(n), A127202(n+1)).

1, 2, 1, 3, 1, 5, 1, 7, 2, 1, 3, 1, 11, 1, 13, 1, 3, 2, 1, 17, 1, 19, 2, 1, 3, 1, 23, 1, 5, 3, 1, 4, 1, 29, 1, 31, 1, 3, 1, 5, 1, 37, 1, 3, 1, 41, 1, 43, 2, 1, 3, 1, 47, 1, 7, 2, 1, 3, 2, 1, 53, 1, 5, 3, 1, 59, 1, 61, 1, 3, 2, 1, 5, 1, 67, 2, 1, 3, 1, 71, 1, 73, 1, 3, 2, 1, 7, 1, 79, 2, 1, 3, 1, 83, 1, 5, 2

Offset: 1

Author

Leroy Quet, Jan 08 2007

Keywords

• nonn

Comments

a(n) never equals a(n+1), by decree.

For the first 719 terms this coincides with the sequence {gcd(A280985(n), A280985(n+1))}. By decree, the latter may not contain two consecutive 1's. - N. J. A. Sloane, Jan 21 2017

Links

• Rémy Sigrist, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A127202, A280985.

Programs

Mathematica

f[l_List] := Block[{k = 1, c = GCD[l[[ -1]], l[[ -2]]]},While[MemberQ[l, k] || GCD[k, l[[ -1]]] == c, k++ ];Append[l, k]]; GCD @@@ Partition[Nest[f, {1, 2}, 100], 2, 1] (* Ray Chandler, Jan 16 2007 *)

Extensions

Extended by Ray Chandler, Jan 16 2007