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

1,2

Comments

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

Links

Table of n, a(n) for n=1..71.

Formula

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

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 *)

Crossrefs

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

Sequence in context: A264921 A098990 A336453 * A117361 A228787 A354103

Adjacent sequences: A162192 A162193 A162194 * A162196 A162197 A162198

Keyword

easy,nonn

Author

Omar E. Pol, Jul 04 2009

Extensions

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

Status

approved