A181732 - OEIS

%I #32 Sep 08 2022 08:45:54

%S 2,3,6,7,9,11,13,17,18,20,24,25,26,28,31,33,34,37,39,41,45,47,51,54,

%T 55,62,65,68,69,70,72,73,74,76,84,86,89,90,91,94,96,97,98,100,101,102,

%U 107,108,109,110,117,119,121,123,124,125,130,133,136,138,139,140

%N Numbers n such that 90n + 1 is prime.

%H Alois P. Heinz, <a href="/A181732/b181732.txt">Table of n, a(n) for n = 1..10000</a>

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

%F a(n) ~ (4/15) n log n. - _Charles R Greathouse IV_, Jun 01 2016, corrected Sep 05 2016

%p a:= proc(n) option remember; local k;

%p        for k from 1+ `if`(n=1, 1, a(n-1))

%p        while not isprime(90*k+1) do od; k

%p     end:

%p seq(a(n), n=1..100);  # _Alois P. Heinz_, Dec 05 2011

%t Select[Range[200], PrimeQ[90 # + 1] &] (* _Vincenzo Librandi_, Sep 06 2016 *)

%o (PARI) is(n)=n%90==1 && isprime(n) \\ _Charles R Greathouse IV_, Jun 01 2016

%o (Magma) [n: n in [0..200]| IsPrime(90*n+1)]; // _Vincenzo Librandi_, Sep 06 2016

%Y Cf. A142312. Complement of A255491.

%K nonn,easy

%O 1,1

%A _J. W. Helkenberg_, Nov 16 2010

%E New name from _Michael B. Porter_, Jul 26 2013