A090082 Even pseudoprimes to base 5.

4, 124, 5662, 11476, 59356, 80476, 91636, 250876, 261964, 482516, 1385836, 1892458, 1926676, 2428084, 2589796, 3743476, 4101796, 6797764, 9155476, 10701076, 10743436, 11263396, 13799836, 13859956, 15570556, 20396476

Offset: 1

Author

Labos Elemer, Nov 25 2003

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..910 (terms below 10^12, calculated from the b-file at A005936; terms 1..100 from Charles R Greathouse IV)
• Index entries for sequences related to pseudoprimes.

Crossrefs

Cf. A005936.

Programs

Mathematica

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

PARI

is(n)=Mod(5,n)^(n-1)==1&&!isprime(n)&&n%2==0 \\ Charles R Greathouse IV, Apr 12 2012

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

Extensions

More terms from Farideh Firoozbakht, Sep 13 2006