A338477 Numbers k such that 398*k^2 - 1 is prime.
1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 17, 18, 19, 20, 22, 24, 25, 27, 28, 29, 33, 34, 37, 38, 43, 44, 46, 47, 51, 52, 54, 55, 58, 59, 60, 67, 68, 71, 73, 75, 79, 80, 81, 82, 83, 85, 86, 87, 89, 90, 93, 94, 95, 96, 97, 100, 103, 106, 107, 108, 110, 112, 114, 116, 117, 119, 121, 124, 125, 128
Offset: 1
Keywords
Examples
a(3)=4 is in the sequence because 398*4^2 - 1 = 6367 is prime.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
- V. Granville, Quadratic progressions with very high prime density, MathOverflow.
Programs
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Maple
select(t -> isprime(398*t^2-1), [$1..1000]);
Formula
a(n) = sqrt(A338476(n) + 1)/398.
Comments