cp's OEIS Frontend

A271612 Number of ways to reciprocally link elements of an n X n X n triangular array with themselves or a neighbor, with no more than 3 elements linked to themselves.

%I A271612 #8 Jun 18 2017 12:44:28
%S A271612 1,4,17,114,2571,42702,216318,5622392,1491326272,101843558868,
%T A271612 1038614548176,131929454285752,334070494079203752,
%U A271612 109915013016304822208,3147612978951707912144,2069163709506683013857472,44655320458467210977882177104,75051772861714827753881814035744
%N A271612 Number of ways to reciprocally link elements of an n X n X n triangular array with themselves or a neighbor, with no more than 3 elements linked to themselves.
%C A271612 Column 3 of A271617.
%F A271612 a(n) = Sum_{i=0..1} A288852(n,floor(n*(n+1)/4)-i). - _Alois P. Heinz_, Jun 18 2017
%e A271612 Some solutions for n=4
%e A271612 .....5........5........0........5........6........5........6........5
%e A271612 ....2.6......2.5......6.6......2.6......5.1......2.6......0.1......2.5
%e A271612 ...0.6.1....5.2.6....5.1.1....4.3.1....2.0.5....0.5.1....4.3.5....6.2.5
%e A271612 ..4.3.1.0..2.0.0.1..2.0.4.3..0.0.4.3..4.3.2.0..0.2.4.3..4.3.2.0..0.1.2.0
%e A271612 Element moves: 0=itself 1=nw 2=ne 3=w 4=e 5=sw 6=se, reciprocals total 7
%Y A271612 Cf. A271617, A288852.
%K A271612 nonn
%O A271612 1,2
%A A271612 _R. H. Hardin_, Apr 10 2016
%E A271612 a(16)-a(18) from _Alois P. Heinz_, Jun 15 2017