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%I #12 Sep 15 2014 14:12:04
%S 3,5,7,8,9,11,12,13,15,17,18,19,21,22,23,25,27,28,29,30,31,32,33,34,
%T 35,37,38,39,41,42,43,44,45,46,47,48,49,50,51,52,53,55,57,58,59,60,61,
%U 62,63,64,65,67,68,69,70,71,72,73,75,76,77,78,79,80,81,82,83,85,86,87,88
%N Numbers n such that n^2 + 1 is composite.
%F a(n) ~ n. - _Charles R Greathouse IV_, Sep 15 2014
%e a(1)=3, because 3^2 + 1 = 10 is composite,
%e a(2)=5, because 5^2 + 1 = 26 is composite,
%e a(3)=7, because 7^2 + 1 = 50 is composite.
%p ts_fn2:=proc(n) local i,tren,ans; ans:=[ ]: for i from 1 to n do tren := i^(2)+1: if (isprime(tren) = false) then ans:=[ op(ans), i ]: fi od: RETURN(ans) end: ts_fn2(200);
%t Select[Range@100,!PrimeQ[#^2+1]&] (* _Vladimir Joseph Stephan Orlovsky_, Feb 03 2012 *)
%o (PARI) is(n)=!isprime(n^2+1) \\ _Charles R Greathouse IV_, Sep 15 2014
%Y Cf. A002496, A002808, A005574, A018252.
%K nonn,easy
%O 1,1
%A _Jani Melik_, Jan 18 2008
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