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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A238983 Numbers n such that the sum of n-th powers of unitary divisors of n is congruent to -1 modulo n. 2
1, 2, 265, 49217, 7870171, 592258417 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(7) > 10^10. - Hiroaki Yamanouchi, Oct 02 2014

LINKS

Table of n, a(n) for n=1..6.

MATHEMATICA

AA[n_, k_] := AA[n, k] = Mod[Sum[If[GCD[i, n] == i && GCD[i, n/i] == 1, PowerMod[i, k, n], 0], {i, n}], n]; Select[Range[1000], Mod[AA[#, #], #] == #-1 &]

PROG

(PARI) isok(n) = (sumdiv(n, d, d^n*(gcd(d, n/d) == 1)) % n) == (n-1); \\ Michel Marcus, Sep 30 2014

(PARI) isok(n) = sumdiv(n, d, if (gcd(d, n/d) == 1, Mod(d, n)^n)) == Mod(n-1, n); \\ Michel Marcus, Oct 02 2014

CROSSREFS

Cf. A034448, A238981, A238982.

Sequence in context: A216984 A007082 A135388 * A188964 A278771 A318171

Adjacent sequences:  A238980 A238981 A238982 * A238984 A238985 A238986

KEYWORD

nonn,more,hard

AUTHOR

José María Grau Ribas, Mar 07 2014

EXTENSIONS

a(4)-a(5) from Hiroaki Yamanouchi, Sep 30 2014

a(6) from Hiroaki Yamanouchi, Oct 02 2014

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 October 15 15:14 EDT 2019. Contains 328030 sequences. (Running on oeis4.)