A181732 Numbers n such that 90n + 1 is prime.

2, 3, 6, 7, 9, 11, 13, 17, 18, 20, 24, 25, 26, 28, 31, 33, 34, 37, 39, 41, 45, 47, 51, 54, 55, 62, 65, 68, 69, 70, 72, 73, 74, 76, 84, 86, 89, 90, 91, 94, 96, 97, 98, 100, 101, 102, 107, 108, 109, 110, 117, 119, 121, 123, 124, 125, 130, 133, 136, 138, 139, 140

Offset: 1

Author

J. W. Helkenberg, Nov 16 2010

Keywords

• nonn
• easy

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A142312. Complement of A255491.

Programs

Magma

[n: n in [0..200]| IsPrime(90*n+1)]; // Vincenzo Librandi, Sep 06 2016

Maple

a:= proc(n) option remember; local k;
       for k from 1+ `if`(n=1, 1, a(n-1))
       while not isprime(90*k+1) do od; k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Dec 05 2011

Mathematica

Select[Range[200], PrimeQ[90 # + 1] &] (* Vincenzo Librandi, Sep 06 2016 *)

PARI

is(n)=n%90==1 && isprime(n) \\ Charles R Greathouse IV, Jun 01 2016

Formula

a(n) = (1/90) [A142312(n) - 1].

a(n) ~ (4/15) n log n. - Charles R Greathouse IV, Jun 01 2016, corrected Sep 05 2016

Extensions

New name from Michael B. Porter, Jul 26 2013