A086806 Sarrus numbers k such that k-1 and k+1 have the same number of prime divisors (counted with multiplicity).

341, 13747, 19951, 35333, 60787, 137149, 150851, 387731, 458989, 617093, 769757, 1104349, 1251949, 1277179, 1397419, 1463749, 1507963, 1826203, 2134277, 2205967, 2617451, 2976487, 3345773, 4361389, 6474691, 6955541, 8095447

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

341 is a pseudoprime to base 2 while 340 = 2^2*5*17 and 342 = 2*3^2*19 each have four primes dividing them.

Mathematica

PrimeFactorExponentsAdded[n_] := Plus @@ Flatten[ Table[ # [[2]], {1}] & /@ FactorInteger[n]]; Select[ Range[9224390], !PrimeQ[ # ] && PowerMod[2, # - 1, # ] == 1 && PrimeFactorExponentsAdded[ # - 1] == PrimeFactorExponentsAdded[ # + 1] & ]

Crossrefs

Intersection of A001567 and A280382.

Cf. A001222.

Sequence in context: A210454 A069309 A353021 * A300327 A289305 A309285

Adjacent sequences: A086803 A086804 A086805 * A086807 A086808 A086809

Keyword

nonn

Author

Jason Earls, Aug 05 2003

Extensions

More terms from Robert G. Wilson v, Aug 13 2003

Status

approved