|
|
A125258
|
|
Smallest prime divisor of n^4-n^2+1.
|
|
3
|
|
|
13, 73, 241, 601, 13, 13, 37, 6481, 9901, 13, 20593, 28393, 37, 13, 97, 83233, 229, 13, 13, 61, 157, 37, 13, 390001, 181, 530713, 13, 37, 809101, 922561, 13, 13, 1069, 277, 1678321, 13, 2083693, 2311921, 61, 13, 673, 3416953, 1753, 13, 13, 1213, 5306113
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
2,1
|
|
COMMENTS
|
All divisors of n^4-n^2+1 are congruent to 1 modulo 12.
a(n) = 13 if and only if n is congruent to 2, -2, 6, or -6 modulo 13.
|
|
REFERENCES
|
K. Ireland and M. Rosen, A Classical Introduction to Modern Number Theory, Springer-Verlag, NY, Second Edition (1990), p. 63.
|
|
LINKS
|
|
|
EXAMPLE
|
The prime divisors of 6^4-6^2+1=1261 are 13 and 97, so a(5) = 13.
|
|
MATHEMATICA
|
Table[FactorInteger[n^4-n^2+1][[1, 1]], {n, 2, 50}] (* Harvey P. Dale, Feb 27 2012 *)
|
|
PROG
|
(PARI) vector(49, n, if(n<2, "-", factor(n^4-n^2+1)[1, 1]))
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|