A256918 Greatest common divisors of adjacent terms in A257218.

1, 1, 3, 2, 4, 2, 5, 5, 3, 9, 6, 4, 8, 6, 10, 20, 8, 16, 12, 9, 27, 18, 12, 15, 15, 25, 25, 10, 7, 7, 14, 14, 21, 21, 63, 42, 28, 56, 16, 32, 24, 40, 20, 50, 30, 18, 27, 81, 54, 72, 24, 28, 35, 35, 105, 30, 45, 45, 75, 100, 40, 32, 64, 48, 48, 36, 63, 189

Offset: 1

Author

Reinhard Zumkeller, Apr 25 2015

Keywords

• nonn

Comments

a(n) = GCD(A257218(n),A257218(n+1)).

Each term occurs at most twice, and it is a plausible conjecture that every term will occur exactly twice.

A257120(n) = position of the first of not more than two occurrences of n: a(A257120(n)) = n;

A257475(n) = position of the second and last occurrence of n: a(A257475(n)) = n;

A257478(n) = distance of positions of first and second occurrence of n.

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..25000

Crossrefs

Cf. A257218, A257120, A257475, A257478.

Programs

Haskell

a256918 n = a257218_list !! (n-1)
a256918_list = zipWith gcd a257218_list $ tail a257218_list