%I A107756
%S A107756 1,4,5,6,7,10,13,14,15,16,17,18,19,20,21,22,23,24,25,28,31,32,33,34,37,
%T A107756 40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,
               63,
%U A107756 64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,82,85,86,87,88,91,94,
               95
%N A107756 Numbers n such that Sum_{k=1..n} Catalan(k) == 1 mod 3.
%D A107756 Y. More, Problem 11165, Amer. Math. Monthly, 112 (2005), 568.
%F A107756 Equivalently, numbers n such that base 3 expansion of n+1 contains a 
               2.
%t A107756 Select[ Range[ 100], Mod[ Sum[(2 n)!/n!/(n + 1)!, {n, #}], 3] == 1 &] 
               (from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 14 2005)
%Y A107756 Cf. A000108, A107755, A107757.
%Y A107756 Equals A074940 - 1.
%Y A107756 Sequence in context: A123438 A039024 A065028 this_sequence A080723 A022561 
               A047312
%Y A107756 Adjacent sequences: A107753 A107754 A107755 this_sequence A107757 A107758 
               A107759
%K A107756 nonn,easy
%O A107756 1,2
%A A107756 N. J. A. Sloane (njas(AT)research.att.com), Jun 11 2005