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

2,1

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. - R. J. Mathar, Aug 11 2009

Prog

(PARI) a(n)=(n^14-21*n^12+175*n^10+105*n^8-3416*n^6+7476*n^4-4320*n^2)/5040 \\ Charles R Greathouse IV, Jun 05 2026

Crossrefs

Cf. A159359.

Sequence in context: A152463 A295206 A209608 * A012770 A387100 A332154

Adjacent sequences: A159364 A159365 A159366 * A159368 A159369 A159370

Keyword

nonn,easy

Author

R. H. Hardin, Apr 11 2009

Status

approved