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

Author

Jason Earls, Aug 05 2003

Keywords

• nonn

Examples

			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.
		

Links

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

Crossrefs

Intersection of A001567 and A280382.

Cf. A001222.

Programs

Mathematica

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

Extensions

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