A073351 n^2(n+1)(2n+1)^2(7n+1)/36.

0, 4, 125, 1078, 5220, 18150, 50869, 122500, 263568, 519840, 956725, 1664234, 2762500, 4407858, 6799485, 10186600, 14876224, 21241500, 29730573, 40876030, 55304900, 73749214, 97057125, 126204588, 162307600, 206635000, 260621829

Offset: 0

Author

Michael Somos, Jul 27 2002

Keywords

• nonn
• easy

References

• Mentioned in a problem on p. 334 of Two-Year College Math. Jnl., Vol. 25, 1994.

Links

• Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).

Crossrefs

Cf. A007750.

Formula

a(n)=sum(i=1, n, i^2)*sum(i=n+1, 2*n, i^2).

G.f.: x(4+97x+287x^2+159x^3+13x^4)/(1-x)^7.