A373880 Number of k in the range s(1), ..., s(n-2) such that gcd(k, s(n)) > 1, where s = A373390.

0, 0, 0, 1, 1, 2, 2, 3, 1, 7, 1, 7, 6, 6, 3, 11, 7, 12, 4, 13, 7, 10, 8, 1, 1, 17, 8, 14, 13, 17, 17, 14, 12, 15, 1, 1, 29, 10, 19, 16, 24, 21, 23, 13, 31, 14, 36, 15, 22, 28, 1, 35, 13, 34, 22, 29, 21, 33, 22, 27, 1, 1, 43, 18, 31, 26, 30, 30, 34, 45, 32, 32, 1, 60, 17, 56, 18, 54, 8, 56, 33

Offset

1,6

Comments

It appears that a(n) = 1 exactly when s(n) is 4, 9, or a prime >3. - Michael De Vlieger, Jun 21 2024

Links

Scott R. Shannon, Table of n, a(n) for n = 1..10000

Michael De Vlieger, Log log scatterplot of a(n), n = 1..2^14.

Example

a(8) = 3 as A373390(8) = 14 and 14 shares a factor m > 1 with three previous terms, A373390(2) = 2, A373390(4) = 4, and A373390(6) = 8.

Mathematica

s = Import["https://oeis.org/A373390/b373390.txt", "Data"][[All, -1]] (* set s to contain terms of A373390 *);
Table[Function[{m, w}, Count[w, _?(! CoprimeQ[#, m[[1]]] &)]] @@ TakeDrop[#, -1] &@ s[[;; n]], {n, 120}] (* Michael De Vlieger, Jun 21 2024 *)

Crossrefs

Cf. A373390, A372073, A372072.

Sequence in context: A219865 A016539 A345886 * A220349 A273218 A173160

Adjacent sequences: A373877 A373878 A373879 * A373881 A373882 A373883

Keyword

nonn

Author

Scott R. Shannon, Jun 20 2024

Status

approved