A217468 Composite values of n such that 2^n == 2 (mod n*(n-1)).

91625794219, 8796093022207, 1557609722332488343, 18216643597893471403

Offset: 1

Author

V. Raman, Oct 04 2012

Keywords

• nonn
• hard
• more

Comments

No other terms below 2^64.

The next term is <= 25790417485109157029391019 = A019320(258). - Emmanuel Vantieghem, Dec 01 2014

Terms A019320(k) belongs to this sequence for k in A297412. - Max Alekseyev, Dec 29 2017

Examples

			a(1) = 91625794219 = (2^38 - 2^19 + 1)/3 = A019320(114).
a(2) = 8796093022207 = 2^43 - 1 = A019320(43).
		

Links

• Mersenne Forum, Prime Conjecture

Crossrefs

Cf. A069051, A216822, A219037, A217465.

Intersection of A001567 and { 2*A014945(k) + 1 }.

Programs

PARI

is_A217468(n)={Mod(2,(n-1)*n)^n==2 & !isprime(n)}  \\ - M. F. Hasler, Oct 07 2012