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%I #13 Sep 24 2017 17:28:41
%S 1,1,1,2,1,1,2,1,1,3,1,2,2,1,1,2,4,1,2,1,1,5,1,2,3,1,2,2,1,1,2,4,1,2,
%T 1,1,2,7,1,5,1,2,3,1,3,2,4,1,2,1,1,2,1,1,5,1,10,3,4,3,2,7,1,3,1,2,2,1,
%U 1,3,7,2,2,1,1,2,4,1,2,4,1,5,1,2,3,1
%N a(n) = the least positive integer k such that k^2 + k + N is prime, where N is the n-th positive odd integer.
%C k^2 + k + n for even n is always even and > 2, so is never prime.
%H Charles R Greathouse IV, <a href="/A078770/b078770.txt">Table of n, a(n) for n = 1..10000</a>
%e For n=1, k^2+k+1 is prime for k=1, since it is 3.
%e For n=7, k^2+k+7 is not prime for k=1, but is prime for k=2, since it is 13.
%t lpik[n_]:=Module[{k=1},While[!PrimeQ[k^2+k+n],k++];k]; Table[lpik[n],{n,1,181,2}] (* _Harvey P. Dale_, Sep 24 2017 *)
%o (PARI) lista(nn) = {forstep (n=1, nn, 2, k = 1; while(! isprime(k*k + k + n), k++); print1(k, ", "););} \\ _Michel Marcus_, May 18 2013
%o (PARI) a(n)=my(k=1);while(!isprime(k^2+k+2*n-1),k++);k \\ _Charles R Greathouse IV_, May 19 2013
%K nonn
%O 1,4
%A _Joseph L. Pe_, Jan 09 2003
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