A162993 The second left hand column of triangle A162990.

9, 144, 3600, 129600, 6350400, 406425600, 32920473600, 3292047360000, 398337730560000, 57360633200640000, 9693947010908160000, 1900013614137999360000, 427503063181049856000000, 109440784174348763136000000, 31628386626386792546304000000

Offset

2,1

Links

Table of n, a(n) for n=2..16.

Formula

a(n) = ((n+1)!/2)^2.

a(n) = A001710(n+1)^2.

From Amiram Eldar, Feb 27 2026: (Start)

Sum_{n>=2} 1/a(n) = 4 * BesselI(0, 2) - 9 = 4 * A070910 - 9.

Sum_{n>=2} (-1)^n/a(n) = 1 - 4 * BesselJ(0, 2) = 1 - 4 * A091681. (End)

Mathematica

Array[((#+1)!/2)^2 &, 20, 2] (* Paolo Xausa, Apr 01 2024 *)

Crossrefs

A001044 and A162994 are two other left hand columns.

A001710(n+1) equals the square root of a(n).

Cf. A070910, A091681.

Sequence in context: A393407 A069134 A034829 * A094594 A173213 A223371

Adjacent sequences: A162990 A162991 A162992 * A162994 A162995 A162996

Keyword

easy,nonn

Author

Johannes W. Meijer, Jul 21 2009

Status

approved