login
This site is supported by donations to The OEIS Foundation.

 

Logo

The OEIS is looking to hire part-time people to help edit core sequences, upload scanned documents, process citations, fix broken links, etc. - Neil Sloane, njasloane@gmail.com

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A037226 a(n) = phi(2n+1) / multiplicative order of 2 mod 2n+1. 4
1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 6, 2, 2, 1, 2, 2, 3, 2, 2, 2, 4, 1, 2, 2, 1, 1, 6, 4, 1, 2, 2, 8, 2, 2, 2, 1, 1, 8, 2, 8, 6, 6, 2, 2, 2, 1, 2, 4, 1, 3, 2, 4, 2, 6, 4, 1, 4, 1, 18, 6, 1, 6, 2, 2, 1, 2, 2, 4, 2, 1, 10, 4, 6, 3, 2, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Number of primitive irreducible factors of x^(2n+1) - 1 over integers mod 2. There are no primitive irreducible factors for x^(2n)-1 because it always has the same factors as x^n-1. Considering that A000374 also counts the cycles in the map f(x) = 2x mod n, a(n) is also the number of primitive cycles of that mapping. - T. D. Noe, Aug 01 2003

Equals number of irreducible factors of the cyclotomic polynomial Phi(2n+1,x) over Z/2Z. All factors have the same degree. - T. D. Noe, Mar 01 2008

LINKS

T. D. Noe, Table of n, a(n) for n = 0..10000

Brillhart, John; Lomont, J. S.; Morton, Patrick. Cyclotomic properties of the Rudin-Shapiro polynomials, J. Reine Angew. Math.288 (1976), 37--65. See Table 2. MR0498479 (58 #16589).

FORMULA

a(n) = Sum{d|2n+1} mu((2n+1)/d) A000374(d), the inverse Mobius transform of A000374 - T. D. Noe, Aug 01 2003

a(n) = A037225(n)/A002326(n).

MATHEMATICA

a[n_] := EulerPhi[2n+1]/MultiplicativeOrder[2, 2n+1]; Table[a[n], {n, 0, 100}] (* Jean-Fran├žois Alcover, Dec 10 2015 *)

PROG

(PARI) a(n)=eulerphi(2*n+1)/znorder(Mod(2, 2*n+1)) \\ Charles R Greathouse IV, Dec 29 2013

CROSSREFS

Cf. A000374 (number of irreducible factors of x^n - 1 over integers mod 2), A081844.

Cf. A006694 (cyclotomic cosets of 2 mod 2n+1).

Sequence in context: A187759 A270645 A268059 * A089641 A086995 A220492

Adjacent sequences:  A037223 A037224 A037225 * A037227 A037228 A037229

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified May 28 16:24 EDT 2017. Contains 287241 sequences.