A063845 a(n) = sigma(usigma(n)), where usigma(n) is the sum of unitary divisors of n (A034448) and sigma(n) is the sum of the divisors (A000203).

1, 4, 7, 6, 12, 28, 15, 13, 18, 39, 28, 42, 24, 60, 60, 18, 39, 72, 42, 72, 63, 91, 60, 91, 42, 96, 56, 90, 72, 195, 63, 48, 124, 120, 124, 93, 60, 168, 120, 120, 96, 252, 84, 168, 168, 195, 124, 126, 93, 168, 195, 144, 120, 224, 195, 195, 186

Offset: 1

Author

N. J. A. Sloane, Oct 30 2001

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n=1..1000

Programs

Mathematica

usigma[n_] := DivisorSum[n, Boole[CoprimeQ[#, n/#]]*#& ]; a[n_] := DivisorSigma[1, usigma[n]]; Array[a, 60] (* Jean-François Alcover, Dec 02 2015 *)

PARI

usigma(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)) { for (n=1, 1000, write("b063845.txt", n, " ", sigma(usigma(n))) ) } \\ Harry J. Smith, Sep 01 2009

Formula

a(n) = A000203(A034448(n)). - Michel Marcus, Dec 02 2015