This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A059499 a(n) = |{m : multiplicative order of 2 mod m = n}|. 20
 1, 1, 1, 2, 1, 3, 1, 4, 2, 5, 3, 16, 1, 5, 5, 8, 1, 24, 1, 38, 9, 11, 3, 68, 6, 5, 4, 54, 7, 79, 1, 16, 11, 5, 13, 462, 3, 5, 13, 140, 3, 123, 7, 110, 54, 11, 7, 664, 2, 114, 29, 118, 7, 124, 59, 188, 13, 55, 3, 4456, 1, 5, 82, 96, 5, 353, 3, 118, 11, 485, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS The multiplicative order of a mod m, GCD(a,m)=1, is the smallest natural number d for which a^d = 1 (mod m). See A002326. a(n) is odd iff n is squarefree, A005117. - Thomas Ordowski, Jan 18 2014 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..200 FORMULA a(n) = 1 iff 2^n-1 is noncomposite. a(prime(n)) = 2^A088863(n)-1. - Thomas Ordowski, Jan 16 2014 EXAMPLE a(3) = |{7}| = 1, a(4) = |{5,15}| = 2, a(6) = |{9,21,63}| = 3. MAPLE with(numtheory): a:= n-> add(mobius(n/d)*tau(2^d-1), d=divisors(n)): seq(a(n), n=1..100);  # Alois P. Heinz, May 31 2012 MATHEMATICA a[n_] := Sum[ MoebiusMu[n/d] * DivisorSigma[0, 2^d - 1], {d, Divisors[n]}]; Table[a[n], {n, 1, 71} ] (* Jean-François Alcover, Dec 12 2012 *) CROSSREFS Cf. A001037, A058943, A059912. Column k=2 of A212957. - Alois P. Heinz, Oct 12 2012 Sequence in context: A100053 A029194 A246582 * A113322 A007380 A319162 Adjacent sequences:  A059496 A059497 A059498 * A059500 A059501 A059502 KEYWORD easy,nonn AUTHOR Vladeta Jovovic, Feb 04 2001 EXTENSIONS More terms from John W. Layman, Mar 22 2002 More terms from Alois P. Heinz, May 31 2012 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.

Last modified October 15 22:25 EDT 2019. Contains 328038 sequences. (Running on oeis4.)