|
|
A309499
|
|
Primes p having a record value of least k such that 4*k^2*p^2 + 1 is prime.
|
|
0
|
|
|
2, 11, 17, 19, 283, 919, 1093, 1787, 9521, 181243, 257611, 274243, 857419, 1644871, 3111607, 6027277, 10452083, 14490703, 36102991, 47352131, 121431767, 171236887, 339934099, 584698243, 1177972427, 3008777311, 3091999399
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
The corresponding record values of k are 1, 3, 5, 15, 20, 22, 24, 45, 95, 104, 115, 116, 135, 143, 155, 165, 179, 186, 190, 245, 250, 260, 277, 284, 310, 313, 335, ...
Gagola calculated the values of k for all the primes below 5000, and noticed that the largest value of k was only 45.
|
|
LINKS
|
Gloria Gagola, Progress on primes, News and Letters, Mathematics Magazine, Vol. 54, No. 1 (1981), p. 43.
|
|
EXAMPLE
|
For the primes p = 2, 3, 5, and 7, 4*p^2 + 1 = 17, 37, 101, and 197 are all primes with k = 1. 11 is the first prime with a value of k = 3, since 4*1*11^2 + 1 = 45 and 4*2^2*11^2 + 1 = 1937 are both composites, and 4*3^2*11^2 + 1 = 4357 is prime.
|
|
MATHEMATICA
|
a[p_] := Module[{k = 1}, While[!PrimeQ[4 * k^2 * p^2 + 1], k++]; k]; s={}; am = 0; p = 1; Do[p = NextPrime[p]; a1 = a[p]; If[a1 > am, am=a1; AppendTo[s, p]], {n, 1, 20000}]; s
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|