A217835 - OEIS

A217835

Fermat pseudoprimes to base 2 that can be written as p^2*n - p*n + p, where p is also a Fermat pseudoprime to base 2 and n is a positive integer.

348161, 831405, 1246785, 1275681, 2077545, 2513841, 5977153, 9613297, 13333441, 13823601, 18137505, 19523505, 21474181, 21880801, 37695505, 38171953, 44521301, 47734141, 54448153, 72887585, 75151441, 95423329

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OFFSET

1,1

COMMENTS

After a(22) = 95423329, no more terms through 10^8.

The corresponding (p,n): (341,3), (645,2), (645,3), (341,11), (645,5), (561,8), (1729,2), (1387,5), (341,120), (561,44), (1905,5), (645,47), (3277,2), (2701,3), (2047,9), (4369,2), (341,384), (2821,6), (2047,13), (2465,12), (3277,7), (4369,5).

Conjecture: For any Fermat pseudoprime p to base 2 there are infinitely many Fermat pseudoprimes to base 2 equal to p^2*n - p*n + p, where n is a positive integer.

See the sequence A215343: the generalized formula from there is p^2*n - p*n + p^2, which suggests an extrapolated formula for obtaining some Fermat pseudoprime to base 2 from another: p^2*n - p*n + p^k.

Conjecture: For any Fermat pseudoprime p to base 2 and any positive integer k, there are infinitely many Fermat pseudoprimes to base 2 equal to p^2*n - p*n + p^k, where n is a positive integer.

LINKS

Table of n, a(n) for n=1..22.

Eric Weisstein's World of Mathematics, Poulet Number

CROSSREFS

Cf. A001567, A213812, A215343.

Sequence in context: A254172 A254165 A254454 * A166263 A338515 A069314

Adjacent sequences: A217832 A217833 A217834 * A217836 A217837 A217838

KEYWORD

nonn

AUTHOR

Marius Coman, Oct 12 2012

STATUS

approved