A159367 Number of n X n arrays of squares of integers summing to 7.

4, 540, 18720, 531300, 8583300, 86748088, 623757696, 3483871560, 16023245700, 63174296020, 219752181792, 688950636972, 1978607887620, 5271705817200, 13162584962560, 31050835145616, 69671782148868, 149524133455500

Offset: 2

Author

R. H. Hardin Apr 11 2009

Keywords

• nonn

Comments

All such sequences have holonomic recurrences (cf. comment in A159359). - Georg Fischer, Feb 17 2022

Links

• R. H. Hardin, Table of n, a(n) for n=2..100
• Index entries for linear recurrences with constant coefficients, signature (15, -105, 455, -1365, 3003, -5005, 6435, -6435, 5005, -3003, 1365, -455, 105, -15, 1).

Formula

Empirical: a(n)=n^2*(n-1)*(n+1)*(n^2-2)*(n^2-3)*(n^6-15*n^4+74*n^2+720)/5040. [From R. J. Mathar, Aug 11 2009]