OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1000
EXAMPLE
5400 is in the sequence because 5400 = 2^3*3^3*5^2 and (2^2+2^3)*(3^2+3^3)*(5^2) = 2*5400.
MAPLE
PPsigma := proc(n)
option remember;
local a, pe, p, e, f, i ;
a := 1 ;
for pe in ifactors(n)[2] do
p := op(1, pe) ;
e := op(2, pe) ;
f := 0 ;
for i from 2 to e do
if isprime(i) then
f := f+p^i ;
end if;
end do:
a := a*f ;
end do;
a ;
end proc:
for n from 1 do
if PPsigma(n) = 2*n then
print(n) ;
end if;
end do: # R. J. Mathar, Mar 13 2024
MATHEMATICA
f[p_, e_] := Plus @@ (p^Select[Range[e], PrimeQ]); s[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[300000], s[#] == 2*# &] (* Amiram Eldar, Sep 19 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Yasutoshi Kohmoto, Jun 24 2004
EXTENSIONS
Corrected and extended by Farideh Firoozbakht, Nov 17 2004
More terms from Amiram Eldar, Sep 19 2022
STATUS
approved