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Prime power perfect numbers: If n = Product p_i^r_i let PPsigma(n) = Product {Sum p_i^s_i, 2<=s_i<=r_i, s_i is prime}; sequence gives numbers k such that PPsigma(k) = 2*k.
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%I #13 Mar 13 2024 11:01:39

%S 216,5400,10584,26136,36504,62424,77976,114264,181656,207576,264600,

%T 295704,363096,399384,477144,606744,653400,751896,803736,912600,

%U 969624,1088856,1149984,1151064,1280664,1348056,1488024,1560600,1710936,1788696,1949400,2032344,2203416

%N Prime power perfect numbers: If n = Product p_i^r_i let PPsigma(n) = Product {Sum p_i^s_i, 2<=s_i<=r_i, s_i is prime}; sequence gives numbers k such that PPsigma(k) = 2*k.

%H Amiram Eldar, <a href="/A096290/b096290.txt">Table of n, a(n) for n = 1..1000</a>

%e 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.

%p PPsigma := proc(n)

%p option remember;

%p local a, pe, p, e,f,i ;

%p a := 1 ;

%p for pe in ifactors(n)[2] do

%p p := op(1, pe) ;

%p e := op(2, pe) ;

%p f := 0 ;

%p for i from 2 to e do

%p if isprime(i) then

%p f := f+p^i ;

%p end if;

%p end do:

%p a := a*f ;

%p end do;

%p a ;

%p end proc:

%p for n from 1 do

%p if PPsigma(n) = 2*n then

%p print(n) ;

%p end if;

%p end do: # _R. J. Mathar_, Mar 13 2024

%t 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 *)

%Y Cf. A100509.

%K nonn

%O 1,1

%A _Yasutoshi Kohmoto_, Jun 24 2004

%E Corrected and extended by _Farideh Firoozbakht_, Nov 17 2004

%E More terms from _Amiram Eldar_, Sep 19 2022