OFFSET
0,2
LINKS
Paolo Xausa, Table of n, a(n) for n = 0..10000
Eric Weisstein's World of Mathematics, Figurate Number.
Eric Weisstein's World of Mathematics, Truncated Octahedron.
Wikipedia, Ehrhart polynomial.
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
FORMULA
a(n) = 32*n^3 + 18*n^2 + 6*n + 1.
G.f.: (19*x^3 + 119*x^2 + 53*x + 1) / (x-1)^4. - Paolo Xausa, Apr 02 2024
E.g.f.: exp(x)*(1 + 56*x + 114*x^2 + 32*x^3). - Stefano Spezia, Apr 02 2024
EXAMPLE
The a(1) = 57 lattice points are all permutations of the points (0,0,0),(0,0,1),(0,0,2),(0,1,1),(0,1,2),(1,1,1), where any number of the coordinates can also be made negative (e.g., (1,-1,0)).
MATHEMATICA
Array[32*#^3 + 18*#^2 + 6*# + 1 &, 50, 0] (* or *)
LinearRecurrence[{4, -6, 4, -1}, {1, 57, 341, 1045}, 50] (* Paolo Xausa, Apr 02 2024 *)
PROG
(Python)
def A371515(n): return n*(n*(32*n+18)+6)+1 # Chai Wah Wu, Apr 02 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Peter Kagey, Mar 25 2024
STATUS
approved