A036368 - OEIS

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A036368

Number of chiral orthoplex n-ominoes in n-2 space.

0, 0, 4, 14, 37, 110, 324, 888, 2368, 6336, 16874, 44414, 116181, 303362, 790157, 2051880, 5317599, 13764133, 35586766, 91910082, 237183164, 611701614, 1576773162, 4062606255, 10463699696, 26942811809, 69358469092

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OFFSET

4,3

COMMENTS

Orthoplex polyominoes are multidimensional polyominoes that do not extend more than two units along any axis.

LINKS

Table of n, a(n) for n=4..30.

FORMULA

G.f.: (C^2(x) + C(-x^2))^2/8 - C^2(-x^2)/4 - C(-x^4)/4 + C^5(x)/(2-2C(x)) - (C(x)+C(-x^2))*C^2(-x^2)/(2-2C(-x^2)) where C(x) is the generating function for chiral n-ominoes in n-1 space, one cell labeled in A045648.

EXAMPLE

a(6)=4 because there are 4 pairs of chiral hexominoes in 2^4 space.

MATHEMATICA

sc[ n_, k_ ] := sc[ n, k ]=c[ n+1-k, 1 ]+If[ n<2k, 0, sc[ n-k, k ](-1)^k ]; c[ 1, 1 ] := 1;

c[ n_, 1 ] := c[ n, 1 ]=Sum[ c[ i, 1 ]sc[ n-1, i ]i, {i, 1, n-1} ]/(n-1);

c[ n_, k_ ] := c[ n, k ]=Sum[ c[ i, 1 ]c[ n-i, k-1 ], {i, 1, n-1} ];

Table[ c[ i, 4 ]/8+Sum[ c[ i, j ], {j, 5, i} ]/2-If[ OddQ[ i ], 0,

c[ i/2, 2 ](-1)^(i/2)/8+If[ OddQ[ i/2 ], 0, c[ i/4, 1 ](-1)^(i/4)/4 ]

+Sum[ c[ i/2, j ](-1)^(i/2), {j, 3, i/2} ]/2 ]+Sum[ c[ j, 1 ]c[ i-2j, 2 ](-1)^j/4

-Sum[ If[ OddQ[ k ], c[ j, (k-1)/2 ]c[ i-2j, 1 ](-1)^j/2, 0 ], {k, 5, i} ],

{j, 1, (i-1)/2} ], {i, 4, 30} ]

CROSSREFS