A061525 Surround numbers of an n X 2 rectangle when n is odd.

83, 361, 951, 1997, 3667, 6153, 9671, 14461, 20787, 28937, 39223, 51981, 67571, 86377, 108807, 135293, 166291, 202281, 243767, 291277, 345363, 406601, 475591, 552957, 639347, 735433, 841911, 959501, 1088947, 1231017, 1386503, 1556221

Offset: 1

Author

Jason Earls, May 03 2001

Keywords

• easy
• nonn

Comments

See A061524 for even n.

Links

• E. J. Friedman, Math. Magic: May, 1999

Crossrefs

Cf. A047875 A061524.

Formula

a(n) = (n^4 + 32n^3 + 278n^2 + 656n + 361)/16 when n is odd.

From Chai Wah Wu, Dec 20 2019: (Start)

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n > 5.

G.f.: x*(3*x^4 - 22*x^3 + 24*x^2 + 54*x - 83)/(x - 1)^5. (End)

Extensions

More terms from Larry Reeves (larryr(AT)acm.org), May 07 2001