A162195 Sum of proper divisors of n-th nonprime number A018252(n).

0, 3, 6, 7, 4, 8, 16, 10, 9, 15, 21, 22, 11, 14, 36, 6, 16, 13, 28, 42, 31, 15, 20, 13, 55, 22, 17, 50, 54, 40, 33, 26, 76, 8, 43, 21, 46, 66, 17, 64, 23, 32, 108, 34, 41, 63, 19, 78, 58, 27, 74, 123, 40, 49, 64, 19, 90, 106, 40, 44, 140, 23, 46, 33, 92, 144, 21, 76, 35, 50, 25

Offset: 1

Author

Omar E. Pol, Jul 04 2009

Keywords

• easy
• nonn

Comments

The k-th positive integer of this sequence is equal to the sum of proper divisors of k-th composite number A002808(k).

Crossrefs

Cf. A001065, A018252, A002808, A162194, A162196.

Programs

Mathematica

NonPrime[n_Integer] := FixedPoint[n + PrimePi@# &, n + PrimePi@n]; f[n_] := Block[{m = NonPrime@n}, DivisorSigma[1, m] - m]; Array[f, 71] (* Robert G. Wilson v, Aug 17 2009 *)
Table[If[PrimeQ[n],-1,Total[Most[Divisors[n]]]],{n,100}]/.(-1->Nothing) (* Harvey P. Dale, Dec 15 2017 *)

Formula

a(n) = A001065(A018252(n)).

Extensions

a(17) and further terms from Robert G. Wilson v, Aug 17 2009