Search: id:A138479
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%I A138479
%S A138479 3,3,5,3,3,5,3,5,5,3,3,7,0,3,7,3,3,5,3,7,5,3,5,5,3,3,5,0,3,7,3,3,29,0,
               3,
%T A138479 5,3,5,5,3,5,5,0,3,7,3,3,19,3,3,5,3,5,7,0,5,5,0,3,11,3,5,5,3,3,5,0,11,
               5,
%U A138479 3,3,7,0,3,7,0,3,5,3,11,7,3,5,5,3,3,5,0,7,7,3,3,5,3,3,7,0,11,5,0
%N A138479 a(n) = smallest prime p such that 2n + p^2 is another prime, or 0 if 
               no such prime exists.
%C A138479 For numbers n such that a(n) = 0 see A138685..
%H A138479 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Near-SquarePrime.html">Near-Square Prime</a>
%e A138479 11=2+3^2 hence a(1)=3
%e A138479 13=4+3^2 hence a(2)=3
%e A138479 31=6+5^2 hence a(3)=5
%e A138479 17=8+3^2 hence a(4)=3
%e A138479 19=10+3^2 hence a(5)=3
%e A138479 37=12+5^2 hence a(6)=5
%e A138479 23=14+3^2 hence a(7)=3
%e A138479 41=16+5^2 hence a(8)=5
%e A138479 43=18+5^2 henec a(9)=5
%e A138479 29=20+3^2 hence a(10)=3
%e A138479 31=22+3^2 hence a(11)=3
%e A138479 73=24+7^2 hence a(12)=7
%t A138479 a = {}; Do[ p = 0; While[ (! PrimeQ[ 2*n + Prime[ p + 1 ]2 ]) && (p < 
               1000), p++ ]; If[ p < 1000, AppendTo[ a, Prime[ p + 1 ] ], AppendTo[ 
               a, 0 ] ], {n, 1, 150} ]; a (*Artur Jasinski, Mar 26 2008*)
%t A138479 a[n_]:=If[Mod[n,3]!=1,(For[m=1,!PrimeQ[2n+Prime[m]^2],m++ ]; Prime[m]),
               If[ !PrimeQ[2n+9],0,3]];Table[a[n],{n,100}] - Farideh Firoozbakht 
               (mymontain(AT)yahoo.com), Mar 28 2008
%Y A138479 Cf. A002373, A020481, A049613, A059324 (?).
%Y A138479 Sequence in context: A013606 A054906 A020483 this_sequence A136019 A063714 
               A113965
%Y A138479 Adjacent sequences: A138476 A138477 A138478 this_sequence A138480 A138481 
               A138482
%K A138479 nonn,hard
%O A138479 1,1
%A A138479 Philippe LALLOUET (philip.lallouet(AT)orange.fr), Mar 20 2008
%E A138479 More terms from Artur Jasinski (grafix(AT)csl.pl) and Farideh Firoozbakht 
               (mymontain(AT)yahoo.com), Mar 26 2008

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