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 A225806 Prime(n) such that 2*n^2 - prime(n) is square. 0
 2, 7, 17, 71, 6607, 15313, 91801, 141689, 443777, 858463, 1353593, 2345479, 726919199, 2458927937, 7425764663, 37193744801, 329683117297, 973676004031, 1294734832753, 3825780992497, 10360880429177 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The associated indices n are 1, 4, 7, 20, 854, 1789, 8869, 13157, 37247, 68234, .... a(13) > 6*10^6. - W. Edwin Clark, Jul 25 2013 a(14) > 1.7 * 10^9. - Robert Israel, Apr 13 2020 LINKS EXAMPLE 17 is in the sequence because 17 = prime(7) and 2*7^2 - 17 = 81 is square. MAPLE p:=1: count:= 0: R:= NULL: S:= NULL: for i from 1 while count < 13 do   p:= nextprime(p);   if issqr(2*i^2-p) then     count:= count+1;     R:= R, p;     S:= S, i;   fi od: R; # Robert Israel, Apr 13 2020 PROG (PARI) isok(p) = isprime(p) && issquare(2*primepi(p)^2 - p); \\ Michel Marcus, Apr 14 2020 CROSSREFS Sequence in context: A067602 A216389 A154298 * A283754 A122382 A025554 Adjacent sequences:  A225803 A225804 A225805 * A225807 A225808 A225809 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Jul 29 2013 EXTENSIONS a(5)-a(11) from Harvey P. Dale, Jul 22 2013 a(12) from W. Edwin Clark, Jul 25 2013 a(13) from Robert Israel, Apr 13 2020 a(9) corrected and a(14)-a(21) added by Giovanni Resta, Apr 13 2020 STATUS approved

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Last modified August 13 19:30 EDT 2020. Contains 336451 sequences. (Running on oeis4.)