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

1,3

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

Prog

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

Crossrefs

Cf. A257218, A257120, A257475, A257478.

Sequence in context: A349322 A193295 A356275 * A099871 A157220 A304182

Adjacent sequences: A256915 A256916 A256917 * A256919 A256920 A256921

Keyword

nonn

Author

Reinhard Zumkeller, Apr 25 2015

Status

approved