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

%I A181732 #32 Sep 08 2022 08:45:54
%S A181732 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 A181732 55,62,65,68,69,70,72,73,74,76,84,86,89,90,91,94,96,97,98,100,101,102,
%U A181732 107,108,109,110,117,119,121,123,124,125,130,133,136,138,139,140
%N A181732 Numbers n such that 90n + 1 is prime.
%H A181732 Alois P. Heinz, <a href="/A181732/b181732.txt">Table of n, a(n) for n = 1..10000</a>
%F A181732 a(n) = (1/90) [A142312(n) - 1].
%F A181732 a(n) ~ (4/15) n log n. - _Charles R Greathouse IV_, Jun 01 2016, corrected Sep 05 2016
%p A181732 a:= proc(n) option remember; local k;
%p A181732        for k from 1+ `if`(n=1, 1, a(n-1))
%p A181732        while not isprime(90*k+1) do od; k
%p A181732     end:
%p A181732 seq(a(n), n=1..100);  # _Alois P. Heinz_, Dec 05 2011
%t A181732 Select[Range[200], PrimeQ[90 # + 1] &] (* _Vincenzo Librandi_, Sep 06 2016 *)
%o A181732 (PARI) is(n)=n%90==1 && isprime(n) \\ _Charles R Greathouse IV_, Jun 01 2016
%o A181732 (Magma) [n: n in [0..200]| IsPrime(90*n+1)]; // _Vincenzo Librandi_, Sep 06 2016
%Y A181732 Cf. A142312. Complement of A255491.
%K A181732 nonn,easy
%O A181732 1,1
%A A181732 _J. W. Helkenberg_, Nov 16 2010
%E A181732 New name from _Michael B. Porter_, Jul 26 2013