A078511 Numbers k such that sopfr(k)=tau(k).

2, 60, 72, 168, 270, 450, 560, 990, 1056, 1188, 1470, 2496, 3200, 3402, 3520, 3672, 4788, 5700, 8320, 9856, 9936, 10164, 10395, 11000, 11160, 12180, 12740, 13056, 13720, 14616, 16524, 17400, 17940, 18522, 19380, 20000, 20475, 21252, 21528

Offset

1,1

Comments

It appears Sum_{n=1..m} a(n) =~ c*sqrt(m)*(log(m) - log(log(m))^2), at c ~ 0.038, asymptotically, after examining m up to 10,000,000, with data intervals of 10,000. - Richard R. Forberg, Feb 10 2015

Links

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

Formula

A001414(a(n)) = A000005(a(n)).

Mathematica

s = {}; Do[If[DivisorSigma[0, n] == Total[Times @@@ FactorInteger[n]], AppendTo[s, n]], {n, 2, 22000}]; s (* Amiram Eldar, Jun 22 2019 *)

Prog

(PARI) isok(n) = {my(f = factor(n)); sum(i=1, #f~, f[i, 1]*f[i, 2]) == numdiv(n); } \\ Michel Marcus, Feb 11 2015

Crossrefs

Cf. A000005, A001414.

Sequence in context: A113549 A268432 A117482 * A370881 A354770 A087004

Adjacent sequences: A078508 A078509 A078510 * A078512 A078513 A078514

Keyword

nonn

Author

Benoit Cloitre, Jan 11 2003

Status

approved