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A090740 Exponent of 2 in 3^n - 1. 10
1, 3, 1, 4, 1, 3, 1, 5, 1, 3, 1, 4, 1, 3, 1, 6, 1, 3, 1, 4, 1, 3, 1, 5, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 5, 1, 3, 1, 4, 1, 3, 1, 6, 1, 3, 1, 4, 1, 3, 1, 5, 1, 3, 1, 4, 1, 3, 1, 8, 1, 3, 1, 4, 1, 3, 1, 5, 1, 3, 1, 4, 1, 3, 1, 6, 1, 3, 1, 4, 1, 3, 1, 5, 1, 3, 1, 4, 1, 3, 1, 7, 1, 3, 1, 4, 1, 3, 1, 5, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also the 2-adic order of Fibonacci(3n) [Lengyel]. - R. J. Mathar, Nov 05 2008

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

T. Lengyel, The order of the Fibonacci and Lucas numbers, Fib. Quart. 33 (1995), 234-239.

D. Marques, P. Trojovsky, The p-adic order of some fibonomial coefficients, J. Int. Seq. 18 (2015) # 15.3.1, proposition 7

FORMULA

Multiplicative with a(p^e) = e+2 if p = 2; 1 if p > 2. G.f.: A(x) = 1/(1-x^2) + Sum_{k>=0} x^(2^k)/(1-x^(2^k)). - Vladeta Jovovic, Jan 19 2004

G.f.: Sum_{k>=0} t*(1+2*t+t^2+t^3)/(1-t^4) with t=x^2^k. Recurrence: a(2n) = a(n) + 1 + [n odd], a(2n+1) = 1. - Ralf Stephan, Jan 23 2004

G.f. A(x) satisfies A(x) = A(x^2) + x/(1-x) + x^2/(1-x^4). - Robert Israel, Dec 28 2015

EXAMPLE

n=2: 3^2 - 1 = 8 = 2^3 so a(2)=3.

MAPLE

seq(padic:-ordp(3^n-1, 2), n=1..100); # Robert Israel, Dec 28 2015

MATHEMATICA

Table[Part[Flatten[FactorInteger[ -1+3^n]], 2], {n, 1, 70}]

IntegerExponent[#, 2]&/@(3^Range[110]-1) (* Harvey P. Dale, Jan 28 2017 *)

PROG

(PARI) a(n)=if(n<1, 0, if(n%2==0, a(n/2)+1+(n/2)%2, 1)) /* Ralf Stephan, Jan 23 2004 */

(PARI) a(n)=valuation(fibonacci(3*n), 2); \\ Joerg Arndt, Oct 28 2012

(PARI) a(n)=my(t=valuation(n, 2)); if(t, t+2, 1) \\ Charles R Greathouse IV, Mar 14 2014

CROSSREFS

Cf. A069895, A091512, A088660, A090739, A001511.

a(n) = A007814(n) + A059841(n) + 1.

Sequence in context: A004592 A116992 A233267 * A094603 A165595 A213181

Adjacent sequences:  A090737 A090738 A090739 * A090741 A090742 A090743

KEYWORD

nonn,mult,easy

AUTHOR

Labos Elemer and Ralf Stephan, Jan 19 2004

STATUS

approved

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Last modified October 16 21:10 EDT 2019. Contains 328103 sequences. (Running on oeis4.)