A111020 Indices of Catalan numbers (A000108) that are == 2 mod 3.

2, 3, 4, 8, 9, 10, 26, 27, 28, 38, 39, 40, 80, 81, 82, 92, 93, 94, 110, 111, 112, 116, 117, 118, 242, 243, 244, 254, 255, 256, 272, 273, 274, 278, 279, 280, 326, 327, 328, 332, 333, 334, 350, 351, 352, 362, 363, 364, 728, 729, 730, 740, 741, 742

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

filter:= proc(n) local L1, L2, L3;
  L1:= convert(2*n, base, 3);
  L2:= convert(n, base, 3);
  L3:= convert(n-1, base, 3);
  mul(binomial(L1[i], L2[i]), i=1..nops(L2)) - mul(binomial(L1[i], L3[i]), i=1..nops(L3)) mod 3 = 2
end proc:
select(filter, [$1..1000]); # Robert Israel, Jun 30 2020

Mathematica

Flatten[Position[CatalanNumber[Range[750]], _?(Mod[#, 3]==2&)]] (* Harvey P. Dale, Sep 21 2012 *)

Crossrefs

Cf. A000108.

Sequence in context: A246444 A117847 A045577 * A002971 A157318 A158031

Adjacent sequences: A111017 A111018 A111019 * A111021 A111022 A111023

Keyword

nonn,look

Author

Robert G. Wilson v, Sep 09 2005

Status

approved