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A162195 Sum of proper divisors of n-th nonprime number A018252(n). 2
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 (list; graph; refs; listen; history; text; internal format)
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 A245220

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

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Last modified June 12 22:55 EDT 2021. Contains 344978 sequences. (Running on oeis4.)