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A168493 a(n) = 3^floor(n^2/2). 2
1, 1, 9, 81, 6561, 531441, 387420489, 282429536481, 1853020188851841, 12157665459056928801, 717897987691852588770249, 42391158275216203514294433201, 22528399544939174411840147874772641, 11972515182562019788602740026717047105681 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Hankel transform of A168492. A trivial Somos-4 sequence linked to elliptic curve y^2 = 1 - 16x + 76x^2 - 96x^3.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..50

FORMULA

a(n) = 3^floor(n^2/2) = 9^floor(n^2/4) = 9^A002620(n) = 81*a(n-2)^2/a(n-4).

MATHEMATICA

Table[3^Floor[n^2/2], {n, 0, 20}]  (* Harvey P. Dale, Mar 06 2011 *)

PROG

(MAGMA) [3^Floor(n^2/2): n in [0..15]]; // Vincenzo Librandi, Jul 24 2016

CROSSREFS

Sequence in context: A110853 A167723 A203107 * A003302 A053915 A067216

Adjacent sequences:  A168490 A168491 A168492 * A168494 A168495 A168496

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Nov 27 2009

STATUS

approved

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Last modified February 19 12:48 EST 2018. Contains 299333 sequences. (Running on oeis4.)