cp's OEIS Frontend

A175282 Positive numbers n with property that n^2+3n+9 is prime (A005471).

%I A175282 #8 Jun 06 2019 05:38:01
%S A175282 1,2,4,7,8,10,11,16,17,23,25,28,29,31,32,37,38,43,49,50,56,58,64,70,
%T A175282 73,85,88,91,94,95,98,101,107,112,121,122,127,130,133,134,136,140,142,
%U A175282 143,155,158,163,164,169,172,175,176,179,182,197,200,205,206,212,214,218
%N A175282 Positive numbers n with property that n^2+3n+9 is prime (A005471).
%C A175282 Notice that at n=-1, n^2+3n+9=7 is also (positive) prime.
%H A175282 Erik Dofs, <a href="http://pldml.icm.edu.pl/pldml/element/bwmeta1.element.bwnjournal-number-aa-1995-73-3">Solutions of x^3+y^3+z^3=n*x*y*z</a>, Acta Arithm. 73.3 (1995) 201
%p A175282 A175282 := proc(n)
%p A175282     option remember;
%p A175282     if n = 1 then
%p A175282         1;
%p A175282     else
%p A175282         for a from procname(n-1)+1 do
%p A175282             if isprime(a^2+3*a+9) then
%p A175282                 return a;
%p A175282             end if;
%p A175282         end do;
%p A175282     end if;
%p A175282 end proc: # _R. J. Mathar_, Jun 06 2019
%t A175282 Select[Range[1,400],PrimeQ[ #^2+3*#+9]&]
%Y A175282 Cf. A005471, A175281.
%K A175282 nonn
%O A175282 1,2
%A A175282 _Zak Seidov_, Mar 21 2010