A257533 Sum of the proper divisors of the n-th semiprime.

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, 18, 43, 22, 45, 32, 20, 34, 49, 24, 55, 40, 28, 61, 24, 11, 63, 44, 46, 26, 69, 50, 73, 24, 34, 75, 36, 81, 56, 30, 85, 13, 62, 91, 64, 42, 28, 99, 70

Offset: 1

Author

R. J. Mathar, Apr 28 2015

Keywords

• nonn
• easy

Comments

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

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A083681.

Programs

Maple

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

Mathematica

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

PARI

go(lim)=my(v=List()); forprime(p=2,lim\2, forprime(q=2,min(lim\p,p), listput(v,[p*q,if(qu[2],v) \\ Charles R Greathouse IV, Apr 28 2015

Formula

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

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