OFFSET
1,1
COMMENTS
EXAMPLE
80 is in this sequence since its sum of bi-unitary divisors is 162 = 2 * 80 + 2.
MATHEMATICA
fun[p_, e_] := If[OddQ[e], (p^(e+1)-1)/(p-1), (p^(e+1)-1)/(p-1)-p^(e/2)]; Select[Range[2, 10000], Times@@(fun @@@ FactorInteger[#]) == 2#+2 &]
PROG
(PARI) bsigma(n, f=factor(n))=prod(i=1, #f~, my(p=f[i, 1], e=f[i, 2]); if (e%2, (p^(e+1)-1)/(p-1), (p^(e+1)-1)/(p-1) -p^(e/2)));
forfactored(n=1, 10^8, if(bsigma(n[1], n[2])==2*n[1]+2, print1(n[1]", "))) \\ Charles R Greathouse IV, Nov 29 2018
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Nov 29 2018
EXTENSIONS
a(13) from Giovanni Resta, Dec 01 2018
STATUS
approved