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 A090082 Even pseudoprimes to base 5. 15

%I

%S 4,124,5662,11476,59356,80476,91636,250876,261964,482516,1385836,

%T 1892458,1926676,2428084,2589796,3743476,4101796,6797764,9155476,

%U 10701076,10743436,11263396,13799836,13859956,15570556,20396476

%N Even pseudoprimes to base 5.

%H Charles R Greathouse IV, <a href="/A090082/b090082.txt">Table of n, a(n) for n = 1..100</a>

%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>

%t Do[s=Mod[ -1+5^(n-1), n]; If[Equal[s, 0]&&!PrimeQ[n]&&EvenQ[n], Print[n]], {n, 1, 1000000}]

%o (PARI) is(n)=Mod(5,n)^(n-1)==1&&!isprime(n)&&n%2==0 \\ _Charles R Greathouse IV_, Apr 12 2012

%o (PARI) p=2;forprime(q=3,1e8,forstep(n=p+1,q-1,2,if(Mod(5,n)^(n-1)==1,print1(n", ")));p=q) \\ _Charles R Greathouse IV_, Apr 12 2012

%Y Cf. A005936.

%K nonn

%O 1,1

%A _Labos Elemer_, Nov 25 2003

%E More terms from _Farideh Firoozbakht_, Sep 13 2006

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Last modified August 7 23:50 EDT 2022. Contains 355995 sequences. (Running on oeis4.)