Q. about triangle A106239 (graphs with unicyclic components)
N. J. A. Sloane
njas at research.att.com
Mon Feb 25 03:07:43 CET 2008
>%S A107755 2,8,12,26,30,36,38,80,84,90,92,108,110,116,120,242,246,252,254,270,272,
>%N A107755 Numbers n such that Sum_{k=1..n} Catalan(k) == 0 mod 3.
>%Y A107755 Equals 2*A074938.
This %Y is obviously wrong (A074938 = "odd numbers such that...", but
here are multiples of 4).
Indeed all elements of this sequence are even, but the halved sequence
%I A000001
%S A000001 1, 4, 6, 13, 15, 18, 19, 40, 42, 45, 46, 54, 55, 58, 60,
121, 123, 126, 127, 135, 136, 139, 141, 162, 163, 166, 168, 175, 177,
180, 181, 364, 366, 369, 370, 378, 379, 382, 384, 405, 406, 409, 411,
418, 420, 423, 424, 486, 487, 490, 492, 499, 501, 504, 505
%N A000001 Numbers n such that Sum_{k=1..2n} Catalan(k) == 0 mod 3.
%Y A000001 Equals (1/2) A107755.
does not yet exist on OEIS.
M.H.
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