OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (3,-2,-1,0,1,2,-3,1).
FORMULA
a(n) = (1/288)*(7+9*(-1)^n-16*(-1)^(n mod 3)+24*n+124*n^2+104*n^3+22*n^4).
G.f.: x*(1+3*x+4*x^2+3*x^3)/((1+x)*(1+x+x^2)*(1-x)^5). - Bruno Berselli, Sep 11 2012
EXAMPLE
For n=3, the number of tetrahedra of any orientation and size is t(3)+t(1)=15+1=16 and the number of octahedra of any size is t(2)=4 the total number being a(n)=20, where t(n) denotes the tetrahedral number A000292(n).
MATHEMATICA
Table[(1/288) (7 + 9 (-1)^n - 16 (-1)^Mod[n, 3] + 24 n + 124 n^2 + 104 n^3 + 22 n^4), {n, 50}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
V.J. Pohjola, Sep 03 2012
STATUS
approved