login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A000117 Number of even sequences with period 2n (bisection of A000011).
(Formerly M1150 N0438)
3
1, 2, 4, 8, 18, 44, 122, 362, 1162, 3914, 13648, 48734, 176906, 649532, 2405236, 8964800, 33588234, 126390032, 477353376, 1808676326, 6872485104, 26179922024, 99957747388, 382443112538, 1466024067850, 5629516646996, 21651955485304, 83400061453514 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..500

E. N. Gilbert and J. Riordan, Symmetry types of periodic sequences, Illinois J. Math., 5 (1961), 657-665.

MATHEMATICA

b[0] = 1; b[n_] := (2^Floor[n/2] + (Table[EulerPhi[2d]*2^(n/d)/(2n), {d, Divisors[n]}] // Accumulate // Last))/2; a[n_] := b[2n]; Table[a[n], {n, 0, 30}] (* Jean-Fran├žois Alcover, Mar 07 2014 *)

CROSSREFS

Sequence in context: A006786 A125809 A245176 * A308030 A252653 A006771

Adjacent sequences:  A000114 A000115 A000116 * A000118 A000119 A000120

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from David W. Wilson, Jan 13 2000

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 30 08:43 EDT 2020. Contains 334712 sequences. (Running on oeis4.)