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

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Mathematica

Select[Range[200], !PrimeQ[2Prime[#]^2 - 1]&]

Prog

(Magma) [n: n in [1..220]| not IsPrime(2*NthPrime(n)^2-1)];

Crossrefs

Cf. A092057, A092058.

Sequence in context: A154927 A348297 A363955 * A276006 A091767 A024549

Adjacent sequences: A220786 A220787 A220788 * A220790 A220791 A220792

Keyword

nonn,easy

Author

Vincenzo Librandi, Jan 18 2013

Status

approved