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A217468
Composite values of n such that 2^n == 2 (mod n*(n-1)).
7
91625794219, 8796093022207, 1557609722332488343, 18216643597893471403
OFFSET
1,1
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
EXAMPLE
a(1) = 91625794219 = (2^38 - 2^19 + 1)/3 = A019320(114).
a(2) = 8796093022207 = 2^43 - 1 = A019320(43).
PROG
(PARI) is_A217468(n)={Mod(2, (n-1)*n)^n==2 & !isprime(n)} \\ - M. F. Hasler, Oct 07 2012
CROSSREFS
Intersection of A001567 and { 2*A014945(k) + 1 }.
Sequence in context: A153433 A234386 A015417 * A234052 A104831 A231235
KEYWORD
nonn,hard,more
AUTHOR
V. Raman, Oct 04 2012
STATUS
approved