A220789 Numbers n such that 2*prime(n)^2 - 1 is not prime.
3, 8, 9, 10, 11, 12, 15, 16, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 32, 34, 35, 36, 38, 39, 40, 43, 44, 48, 49, 50, 51, 52, 53, 55, 57, 58, 60, 61, 63, 65, 66, 67, 68, 69, 70, 72, 74, 76, 77, 78, 79, 82, 83, 85, 86, 87, 88, 89, 90, 91, 92, 94, 95, 96, 97, 98, 99, 100
Offset: 1
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Programs
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Magma
[n: n in [1..220]| not IsPrime(2*NthPrime(n)^2-1)];
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Mathematica
Select[Range[200], !PrimeQ[2Prime[#]^2 - 1]&]