A099202 a(n) = 2^floor(n^2/2).

1, 1, 4, 16, 256, 4096, 262144, 16777216, 4294967296, 1099511627776, 1125899906842624, 1152921504606846976, 4722366482869645213696, 19342813113834066795298816, 316912650057057350374175801344

Offset

0,3

Comments

Hankel transform of A168490. Linked to elliptic curve y^2=1-12x+44x^2-48x^3 through g.f. of A168490.- Paul Barry, Nov 27 2009

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..80

Formula

a(n) = A016116(n) * A006125(n)

a(n) = 16a(n-2)^2 / a(n-4). - Michael Somos, Sep 16 2005

a(n) = 4^floor(n^2/4) = 4^A002620(n). - Paul Barry, Nov 27 2009

Prog

(PARI) a(n)=2^(n^2\2)
(Magma) [2^Floor(n^2/2): n in [0..20]]; // Vincenzo Librandi, Aug 16 2011
(Python)
def A099202(n): return 1<<(n**2>>1) # Chai Wah Wu, Jan 18 2023

Crossrefs

Cf. A002620, A006125, A016116, A168490.

Sequence in context: A232840 A113905 A200045 * A139288 A152921 A215116

Adjacent sequences: A099199 A099200 A099201 * A099203 A099204 A099205

Keyword

easy,nonn

Author

Paul Barry, Oct 04 2004

Status

approved