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Sum of the proper divisors of the n-th semiprime.
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%I #8 Mar 15 2022 14:46:09

%S 2,5,3,7,9,8,10,13,5,15,14,19,12,21,16,25,7,20,16,22,31,33,18,26,39,

%T 18,43,22,45,32,20,34,49,24,55,40,28,61,24,11,63,44,46,26,69,50,73,24,

%U 34,75,36,81,56,30,85,13,62,91,64,42,28,99,70

%N Sum of the proper divisors of the n-th semiprime.

%C For purposes of this sequence, the proper divisors of a number include all divisors other than 1 and the number itself. - _Harvey P. Dale_, Mar 15 2022

%H Charles R Greathouse IV, <a href="/A257533/b257533.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A048050(A001358(n)).

%F A083681(n)-a(n) = A088707(n).

%p seq(A048050(A001358(n)),n=1..80) ;

%t Total[Rest[Most[Divisors[#]]]]&/@Select[Range[250],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Mar 15 2022 *)

%o (PARI) go(lim)=my(v=List()); forprime(p=2,lim\2, forprime(q=2,min(lim\p,p), listput(v,[p*q,if(q<p,p+q,p)]))); v=vecsort(Vec(v),1); apply(u->u[2],v) \\ _Charles R Greathouse IV_, Apr 28 2015

%Y Cf. A083681.

%K nonn,easy

%O 1,1

%A _R. J. Mathar_, Apr 28 2015