A261989 - OEIS

%I #20 Sep 21 2015 06:26:57

%S 1,65,175,20737,32045,41474,64090,128180,207370,207553,352529,415106,

%T 705058,1264957,1762645,1824877,2075530,2529914,3525290,3628975,

%U 3649754,7050580,7590250,10223341,12649570,17626450,20446682,21504269,23723401,36321775,40893364,43008538,45621925

%N Numbers such that A017666(n) = A017668(n).

%H Michel Marcus, <a href="/A261989/b261989.txt">Table of n, a(n) for n = 1..61</a>

%e sigma(65,-1) = 84/65 and sigma(65,-2) = 68/65, both having the same denominator, so 65 is a term.

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

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

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

%K nonn

%O 1,2

%A _Michel Marcus_, Sep 19 2015