cp's OEIS Frontend

A260642 Numbers in A004782, n-1 | C(n-1), but not in A081767, n-1 | C(n), where C(n) = A000108(n) = 2n!/n!(n+1)! are the Catalan numbers.

%I A260642 #15 May 10 2018 09:25:13
%S A260642 3,7,127,511,4095,8191,131071,8388607,33554431,67108863,2147483647,
%T A260642 8589934591,137438953471,2199023255551,17592186044415,35184372088831,
%U A260642 70368744177663,281474976710655,562949953421311,36028797018963967,72057594037927935
%N A260642 Numbers in A004782, n-1 | C(n-1), but not in A081767, n-1 | C(n), where C(n) = A000108(n) = 2n!/n!(n+1)! are the Catalan numbers.
%C A260642 It appears that all terms are of the form 2^k-1 ; see A260641 for the k-values.
%F A260642 a(n) = 2^A260641(n)-1 = A000225(A260641(n)), i.e., equals A000225 o A260641.
%F A260642 Equals A004782 \ A081767.
%Y A260642 Cf. A000108, A260641, A004782, A081767, A014847.
%K A260642 nonn
%O A260642 1,1
%A A260642 _M. F. Hasler_, Nov 11 2015