A008381 floor(n/5)*floor((n+1)/5)*floor((n+2)/5)*floor((n+3)/5).
0, 0, 0, 0, 0, 1, 1, 2, 4, 8, 16, 16, 24, 36, 54, 81, 81, 108, 144, 192, 256, 256, 320, 400, 500, 625, 625, 750, 900, 1080, 1296, 1296, 1512, 1764, 2058, 2401, 2401, 2744, 3136, 3584, 4096, 4096, 4608, 5184, 5832
Offset: 0
Keywords
Formula
a(n) = A002266(n)*A008496(n+1). a(n)= +a(n-1) +4*a(n-5) -4*a(n-6) -6*a(n-10) +6*a(n-11) +4*a(n-15) -4*a(n-16) -a(n-20) +a(n-21). G.f.: x^5*(x^10-2*x^9+4*x^8-4*x^7+8*x^6-8*x^5+8*x^4-4*x^3+4*x^2-2*x+1) * (1+x)^2 / ((x^4+x^3+x^2+x+1)^4 * (1-x)^5). [From R. J. Mathar, Apr 16 2010]