A010697 Period 2: repeat (2,7).

2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2, 7, 2

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

Continued fraction expansion of A176054. - R. J. Mathar, Mar 08 2012

Decimal expansion of 3/11. - Franklin T. Adams-Watters, Nov 21 2018

Links

• Index entries for linear recurrences with constant coefficients, signature (0,1).

Crossrefs

Cf. A010888, A074600.

Programs

Mathematica

Table[-5/2*(-1)^n + 9/2, {n, 0, 120}] (* or *)
Table[7 Mod[n, 2] + 2 Mod[(n + 1), 2], {n, 0, 120}] (* or *)
CoefficientList[Series[(2 + 7 x)/((1 - x) (1 + x)), {x, 0, 120}], x] (* or *)
Table[NestWhile[Total@ IntegerDigits@ # &, 2^n + 5^n, IntegerLength@ # > 1 &], {n, 0, 120}] (* Michael De Vlieger, Jul 13 2016 *)

PARI

a(n)=if(n%2,7,2) \\ Charles R Greathouse IV, Oct 07 2015

Formula

G.f.: (2+7x)/((1-x)(1+x)). - R. J. Mathar, Nov 21 2011

a(n) = A010888(2^n+5^n) = A010888(A074600(n)). - Peter M. Chema, Jul 13 2016

E.g.f.: 7*sinh(x) + 2*cosh(x). - Ilya Gutkovskiy, Jul 14 2016

a(n) = 14/a(n-1). - Nicolas Bělohoubek, Nov 11 2021