A128055 - OEIS

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A128055

a(n) = 2^A128054(n).

1, 1, 2, 4, 8, 32, 64, 64, 128, 256, 512, 2048, 4096, 4096, 8192, 16384, 32768, 131072, 262144, 262144, 524288, 1048576, 2097152, 8388608, 16777216, 16777216, 33554432, 67108864, 134217728, 536870912, 1073741824

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OFFSET

0,3

COMMENTS

A factor in A128056.

The signed sequence 1,1,2,-4,-8,-32,-64,-64,-128,256,512... is the Hankel transform of the doubled sequence 1,1,2,2,6,6,... of central binomial coefficients (A128014). - Paul Barry, Sep 09 2008

LINKS

Table of n, a(n) for n=0..30.

Index entries for linear recurrences with constant coefficients, signature (2,-4,8,-16,32).

FORMULA

G.f.: (-1-16*x^4+4*x^3-4*x^2+x)/((2*x-1)*(4*x^2-2*x+1)*(4*x^2+2*x+1)). - Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009

Sum_{n>=0} 1/a(n) = 62/21. - Amiram Eldar, Mar 28 2023

MATHEMATICA

LinearRecurrence[{2, -4, 8, -16, 32}, {1, 1, 2, 4, 8}, 31] (* James C. McMahon, Jan 05 2025 *)

CROSSREFS

Cf. A128014, A128054, A128056.

Sequence in context: A151406 A307611 A053147 * A061285 A194810 A271216

Adjacent sequences: A128052 A128053 A128054 * A128056 A128057 A128058

KEYWORD

easy,nonn,changed

AUTHOR

Paul Barry, Feb 13 2007

STATUS

approved