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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A290309 Number of units u in Z/nZ such that Phi(5,u) is a unit, where Phi is the cyclotomic polynomial. 1
 1, 1, 2, 2, 3, 2, 6, 4, 6, 3, 6, 4, 12, 6, 6, 8, 16, 6, 18, 6, 12, 6, 22, 8, 15, 12, 18, 12, 28, 6, 26, 16, 12, 16, 18, 12, 36, 18, 24, 12, 36, 12, 42, 12, 18, 22, 46, 16, 42, 15, 32, 24, 52, 18, 18, 24, 36, 28, 58, 12, 56, 26, 36, 32, 36, 12, 66, 32, 44, 18 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS If n is a prime other than 5, then a(n) = n - 5 if n == 1 (mod 10), otherwise a(n) = n - 1. - Robert Israel, Jul 31 2017 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 MAPLE m:=5; T:=[]: for n from 1 to 100 do S:={}: for a from 0 to n-1 do if gcd(a, n)=1 and gcd(cyclotomic(m, a), n)=1 then S:={op(S), a}: fi: od: T:=[op(T), nops(S)]: od: print(T): MATHEMATICA Table[Count[Range[n - 1], k_ /; And[CoprimeQ[k, n], CoprimeQ[Cyclotomic[5, k], n]]], {n, 70}] (* Michael De Vlieger, Jul 30 2017 *) PROG (PARI) a(n) = sum(k=0, n-1, (gcd(n, k)==1) && (gcd(n, polcyclo(5, k))==1)); \\ Michel Marcus, Jul 29 2017 CROSSREFS Cf. A058026 (with Phi(1,u) or Phi(2,u)), A289460 (with Phi(3,u)). Sequence in context: A159688 A128710 A341105 * A095757 A144368 A094438 Adjacent sequences:  A290306 A290307 A290308 * A290310 A290311 A290312 KEYWORD nonn,mult,easy AUTHOR Tristan Phillips, Jordan Lenchitz, Michael Mueller, Madison Wellen, Eric Jovinelly, Joshua Harrington, Jul 27 2017 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 June 16 04:56 EDT 2021. Contains 345056 sequences. (Running on oeis4.)