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A076920
Highest common factor of a pair of successive terms of A076919.
3
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
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
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Oct 17 2002
EXTENSIONS
More terms from R. J. Mathar, Jul 01 2007
STATUS
approved