A087231 a(n) is the smallest number such that the exponent of p=2 factor in 6*a(n)+4 equals n.

1, 4, 6, 2, 26, 10, 106, 42, 426, 170, 1706, 682, 6826, 2730, 27306, 10922, 109226, 43690, 436906, 174762, 1747626, 699050, 6990506, 2796202, 27962026, 11184810, 111848106, 44739242, 447392426, 178956970, 1789569706, 715827882, 7158278826, 2863311530

Offset: 1

Author

Labos Elemer, Aug 28 2003

Keywords

• nonn
• easy

Examples

			n = 10: m = 6*170+4 = 1024 = 2^10, so a(10) = 170.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (1,4,-4)

Crossrefs

Cf. A085058, A087229, A087230.

Programs

PARI

Vec(x*(1 + 3*x - 2*x^2 - 16*x^3 + 16*x^4) / ((1 - x)*(1 - 2*x)*(1 + 2*x)) + O(x^40)) \\ Colin Barker, Mar 16 2017

Formula

For n>2, a(n) = [3/2*2^n - (-2)^n - 2]/3. - Ralf Stephan, May 10 2004

From Colin Barker, Mar 16 2017: (Start)

G.f.: x*(1 + 3*x - 2*x^2 - 16*x^3 + 16*x^4) / ((1 - x)*(1 - 2*x)*(1 + 2*x)).

a(n) = a(n-1) + 4*a(n-2) - 4*a(n-3) for n>5.

(End)