cp's OEIS Frontend

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

%I A373880 #13 Jun 22 2024 15:32:47
%S A373880 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,
%T A373880 17,14,12,15,1,1,29,10,19,16,24,21,23,13,31,14,36,15,22,28,1,35,13,34,
%U A373880 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
%N A373880 Number of k in the range s(1), ..., s(n-2) such that gcd(k, s(n)) > 1, where s = A373390.
%C A373880 It appears that a(n) = 1 exactly when s(n) is 4, 9, or a prime >3. - _Michael De Vlieger_, Jun 21 2024
%H A373880 Scott R. Shannon, <a href="/A373880/b373880.txt">Table of n, a(n) for n = 1..10000</a>
%H A373880 Michael De Vlieger, <a href="/A373880/a373880.png">Log log scatterplot of a(n)</a>, n = 1..2^14.
%e A373880 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.
%t A373880 s = Import["https://oeis.org/A373390/b373390.txt", "Data"][[All, -1]] (* set s to contain terms of A373390 *);
%t A373880 Table[Function[{m, w}, Count[w, _?(! CoprimeQ[#, m[[1]]] &)]] @@ TakeDrop[#, -1] &@ s[[;; n]], {n, 120}] (* _Michael De Vlieger_, Jun 21 2024 *)
%Y A373880 Cf. A373390, A372073, A372072.
%K A373880 nonn
%O A373880 1,6
%A A373880 _Scott R. Shannon_, Jun 20 2024