login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A187025 a(n) is the least number k such that k*n+1 is a prime dividing n^n-1. 2
1, 4, 1, 2, 1, 4, 2, 2, 1, 1436, 1, 4, 501969, 4, 1, 644, 1, 5784852794328402307380, 2, 2, 1, 20, 3, 4, 36, 4, 1, 2, 1, 18353950678197027912484562396837972855962080, 8, 2, 3, 8, 1, 4, 5, 4, 1, 2, 1, 4, 2, 4, 1, 36, 2, 4, 3, 128, 1, 2, 5, 85840, 2, 4, 1, 12, 1, 16, 273 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

COMMENTS

The smallest prime factor of n^n-1 of the form k*n+1 is A187023(n).

LINKS

Table of n, a(n) for n=2..62.

EXAMPLE

7^7-1 = 2*3*29*4733; the smallest prime divisor of the form k*n+1 is 29 = 4*7+1, hence a(7)=4.

MATHEMATICA

Table[p=First/@FactorInteger[n^n-1]; (Select[p, Mod[#1, n] == 1 &, 1][[1]] - 1)/n, {n, 2, 40}]

PROG

(Magma) A187025:=function(n); for d in PrimeDivisors(n^n-1) do if d mod n eq 1 then return (d-1)/n; end if; end for; return 0; end function; [ A187025(n): n in [2..50] ]; // Klaus Brockhaus, Mar 02 2011

CROSSREFS

Cf. A187023, A187024.

Sequence in context: A030787 A176218 A109008 * A074695 A069098 A126241

Adjacent sequences:  A187022 A187023 A187024 * A187026 A187027 A187028

KEYWORD

nonn

AUTHOR

Michel Lagneau, Mar 02 2011

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 6 15:48 EDT 2022. Contains 357269 sequences. (Running on oeis4.)