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Fermat pseudoprimes n to base 3 for which sqrt(8*n + 1) is an integer.
2

%I #31 Jul 03 2017 04:29:19

%S 91,703,1891,2701,7381,8911,10585,12403,16471,18721,29161,38503,41041,

%T 49141,79003,88831,93961,104653,115921,146611,188191,218791,226801,

%U 269011,286903,314821,334153,364231,385003,497503,534061,597871,665281,721801,736291,765703,873181,954271,1056331,1237951

%N Fermat pseudoprimes n to base 3 for which sqrt(8*n + 1) is an integer.

%H Charles R Greathouse IV, <a href="/A217841/b217841.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/FermatPseudoprime.html">Fermat Pseudoprime</a>

%o (PARI) list(lim)=my(v=List(),n); lim\=1; forstep(k=27,sqrtint(8*lim+1),2, n=k^2>>3; if(Mod(3,n)^(n-1)==1, listput(v,n))); Vec(v) \\ _Charles R Greathouse IV_, Jun 30 2017

%Y Cf. A005935, A210461 (subsequence).

%K nonn

%O 1,1

%A _Marius Coman_, Oct 12 2012

%E a(15)-a(18) and a(35) from _Charles R Greathouse IV_, Jun 30 2017