OFFSET
0,2
LINKS
Ray Chandler, Table of n, a(n) for n = 0..1000
Joan Serra-Sagrista, Enumeration of lattice points in l_1 norm, Inf. Proc. Lett. 76 (1-2) (2000) 39-44.
Index entries for linear recurrences with constant coefficients, signature (6, -15, 20, -15, 6, -1).
FORMULA
a(m) = Sum_{k=0..n} 2^k*binomial(n, k)*binomial(m-1, k-1) + 2^n*binomial((n+2*m)/2-1, n-1); with n=6.
From Colin Barker, Apr 14 2012: (Start)
a(n)=(4*n*(31+10*n^2+4*n^4))/15 for n>0.
G.f.: (1+6*x+x^2)*(1+14*x^2+x^4)/(1-x)^6. (End)
PROG
(PARI) a(m) = if (m==0, 1, my(n=6); sum(k=0, n, 2^k*binomial(n, k)*binomial(m-1, k-1)) + 2^n*binomial((n+2*m)/2-1, n-1)); \\ Michel Marcus, Mar 19 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, J. Serra-Sagrista (jserra(AT)ccd.uab.es)
STATUS
approved