A076920 Highest common factor of a pair of successive terms of A076919.

1, 2, 4, 2, 5, 3, 2, 4, 2, 13, 3, 2, 4, 2, 5, 11, 2, 4, 2, 37, 3, 2, 4, 2, 61, 3, 2, 4, 2, 97, 3, 2, 4, 2, 151, 3, 2, 229, 3, 2, 4, 2, 349, 3, 2, 4, 2, 23, 47, 2, 5, 227, 2, 4, 2, 5, 11, 2, 4, 2, 17, 83, 2, 4, 2, 751, 3, 2, 1129, 3, 2, 4, 2, 1699, 3, 2, 2551, 3, 2, 7

Offset

1,2

Links

Table of n, a(n) for n=1..80.

Maple

A076920 := proc(nmax) local a, b, k; a := [1, 2] ; b := [1] ; while nops(b) < nmax do k := op(-1, a)+1 ; while gcd(k, op(-1, a)) <= 1 or gcd(k, op(-1, a)) = gcd(op(-1, a), op(-2, a)) do k := k+1 ; od ; b := [op(b), gcd(k, op(-1, a))] ; a := [op(a), k] ; od ; RETURN(b) ; end: A076920(80) ; # R. J. Mathar, Jul 01 2007

Mathematica

f[1] = 1; f[2] = 2; (* f is A076919 *)
f[n_] := f[n] = Module[{k}, For[k = f[n-1] + 1, True, k++, If[GCD[f[n-1], f[n-2]] != GCD[k, f[n-1]] && GCD[k, f[n-1]] > 1, Return[k]]]];
GCD @@@ Partition[Table[f[n], {n, 1, 81}], 2, 1] (* Jean-François Alcover, Oct 25 2023 *)

Crossrefs

Cf. A076919.

Sequence in context: A238262 A307664 A057037 * A183225 A366586 A020774

Adjacent sequences: A076917 A076918 A076919 * A076921 A076922 A076923

Keyword

nonn

Author

Amarnath Murthy, Oct 17 2002

Extensions

More terms from R. J. Mathar, Jul 01 2007

Status

approved