A103947 a(n) is the number of distinct n-th powers of functions {1, 2} -> {1, 2}.

1, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3

Offset

0,2

Links

Table of n, a(n) for n=0..104.

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

Formula

For n > 2, a(n) = a(n-2).

G.f.: (1+4*x+2*x^2)/(1-x^2). - Jaume Oliver Lafont, Mar 20 2009

Example

a(4) = 3: the four functions {1, 2} -> {1, 2} are f(x) = 1, g(x) = 2, h(x) = x and j(x) = 3 - x. f^4(x) = f(f(f(f(x)))) = 1; so f^4 = f. Similarly, g^4 = g, h^4 = h and j^4 = h, so there are 3 distinct 4th powers.

Mathematica

Join[{1}, LinearRecurrence[{0, 1}, {4, 3}, 104]] (* Ray Chandler, Sep 08 2015 *)

Crossrefs

Cf. A102687, A102709, A103948-A103950.

Cf. A158515. - Jaume Oliver Lafont, Mar 20 2009

Row n=2 of A247026.

Sequence in context: A171783 A251767 A168309 * A178038 A241928 A111048

Adjacent sequences: A103944 A103945 A103946 * A103948 A103949 A103950

Keyword

easy,nonn

Author

David Wasserman, Feb 21 2005

Status

approved