A112752 Greatest common divisors of consecutive terms of numbers of the form 3^i*5^j.

1, 1, 1, 3, 5, 1, 9, 15, 3, 1, 5, 45, 9, 3, 15, 5, 25, 27, 9, 45, 15, 75, 81, 1, 125, 135, 45, 225, 243, 3, 375, 405, 5, 625, 675, 729, 9, 1125, 1215, 15, 1875, 2025, 2187, 1, 3125, 3375, 3645, 45, 5625, 6075, 6561, 3, 9375, 10125, 10935, 5, 15625, 16875, 18225

Offset: 1

Author

Reinhard Zumkeller, Sep 18 2005

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003593, A112757.

Programs

Mathematica

s = {}; m = 12; Do[n = 5^k; While[n <= 5^m, AppendTo[s, n]; n *= 3], {k, 0, m}]; Map[GCD @@ # &, Partition[Union[s], 2, 1]] (* Amiram Eldar, Feb 06 2020 *)

Formula

a(n) = gcd(A003593(n), A003593(n+1)).