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A101921 a(2n) = a(n) + 2n - 1, a(2n+1) = 4n. 12
0, 1, 4, 4, 8, 9, 12, 11, 16, 17, 20, 20, 24, 25, 28, 26, 32, 33, 36, 36, 40, 41, 44, 43, 48, 49, 52, 52, 56, 57, 60, 57, 64, 65, 68, 68, 72, 73, 76, 75, 80, 81, 84, 84, 88, 89, 92, 90, 96, 97, 100, 100, 104, 105, 108, 107, 112, 113, 116, 116, 120, 121, 124, 120, 128 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Exponent of 2 in tangent numbers A000182.

Also, exponent of 2 in the sequences A008775, A009670, A009764, A009798, A012227, A024236, A024277, A024299, A052510.

Also, exponent of 2 in 4^(n-1)/n. [David Brink, Aug 08 2013]

LINKS

Iain Fox, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = 2n - 2 - A007814(n).

G.f.: Sum_{k>=0} t^2(t^2+4t+1)/(1-t^2)^2 where t=x^2^k.

EXAMPLE

G.f. = x^2 + 4*x^3 + 4*x^4 + 8*x^5 + 9*x^6 + 12*x^7 + 11*x^8 + 16*x^9 + 17*x^10 + ...

MATHEMATICA

a[ n_] := If[ n < 1, 0, 2 n - 2 - IntegerExponent[n, 2]]; (* Michael Somos, Mar 02 2014 *)

PROG

(PARI) a(n)=valuation(4^(n-1)/n, 2); \\ Joerg Arndt, Aug 13 2013

CROSSREFS

Equals A007814(A000182(n)).

Sequence in context: A278933 A145447 A204989 * A093340 A046558 A180854

Adjacent sequences:  A101918 A101919 A101920 * A101922 A101923 A101924

KEYWORD

nonn

AUTHOR

Ralf Stephan, Dec 21 2004

STATUS

approved

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Last modified October 19 11:41 EDT 2018. Contains 316359 sequences. (Running on oeis4.)