A236398 Period 4: repeat 1,1,2,1.

1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1

Offset: 1

Author

N. J. A. Sloane, Jan 29 2014

Keywords

• nonn
• easy

References

• H. Blaine Lawson, Jr. and M.-L. Michelsohn, Spin Geometry, Princeton, p. 33.

Links

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

Crossrefs

Cf. A177704, A138191.

Programs

Magma

&cat [[1, 1, 2, 1]^^24]; // Bruno Berselli, Dec 10 2015

PARI

a(n)=n=n%8; if(n==3||n==7, 2, 1) \\ Charles R Greathouse IV, Jul 17 2016

Formula

a(n) = a(n-4) for n > 4. G.f.: x*(1 + x + 2*x^2 + x^3)/(1 - x^4). - Chai Wah Wu, Jun 04 2016

E.g.f.: (-2 - sin(x) + 3*sinh(x) + 2*cosh(x))/2. - Ilya Gutkovskiy, Jun 04 2016

a(n) = (5-cos(n*Pi)-2*sin(n*Pi/2))/4. - Luce ETIENNE, Feb 17 2017

Extensions

Definition corrected by Paul Curtz. - N. J. A. Sloane, Oct 10 2016