A261989 Numbers such that A017666(n) = A017668(n).

1, 65, 175, 20737, 32045, 41474, 64090, 128180, 207370, 207553, 352529, 415106, 705058, 1264957, 1762645, 1824877, 2075530, 2529914, 3525290, 3628975, 3649754, 7050580, 7590250, 10223341, 12649570, 17626450, 20446682, 21504269, 23723401, 36321775, 40893364, 43008538, 45621925

Offset: 1

Author

Michel Marcus, Sep 19 2015

Keywords

• nonn

Examples

			sigma(65,-1) = 84/65 and sigma(65,-2) = 68/65, both having the same denominator, so 65 is a term.
sigma(32045, -1) = 9072/6409 and sigma(32045, -2) = 6736/6409, both having the same denominator, so 32045 is a term.
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..61

Crossrefs

Cf. denominator of sum of powers of divisors of n: A017666 (-1st powers), A017668 (-2nd powers).

Programs

PARI

isok(n) = denominator(sigma(n,-1))==denominator(sigma(n,-2));