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A282512 Denominator of the sum of the reciprocals of the first n nonprimes. 9
1, 4, 12, 24, 72, 360, 360, 2520, 504, 1008, 336, 1680, 1680, 18480, 18480, 92400, 1201200, 10810800, 10810800, 10810800, 21621600, 21621600, 367567200, 52509600, 52509600, 997682400, 997682400, 997682400, 6983776800, 6983776800, 6983776800, 160626866400, 160626866400, 1124388064800, 1124388064800 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..3954

EXAMPLE

The first few fractions are 1, 5/4, 17/12, 37/24, 119/72, 631/360, 661/360, 4807/2520, 995/504, 2053/1008, 703/336, 3599/1680, ... - N. J. A. Sloane, Dec 15 2017

MAPLE

NP:= remove(isprime, [$1..100]):

S:= ListTools:-PartialSums(map(t -> 1/t, NP)):

map(denom, S); # Robert Israel, May 01 2017

MATHEMATICA

With[{nn=50}, Denominator@Accumulate[1/Complement[Range@nn, Prime@Range@PrimePi@nn]]] (* Vincenzo Librandi, May 02 2017 *)

CROSSREFS

Cf. A018252 (nonprime numbers), A282511 (numerators).

The following fractions are all related to each other: Sum 1/n: A001008/A002805, Sum 1/prime(n): A024451/A002110 and A106830/A034386, Sum 1/nonprime(n): A282511/A282512, Sum 1/composite(n): A250133/A296358.

Sequence in context: A215223 A318610 A296358 * A025543 A064354 A199903

Adjacent sequences:  A282509 A282510 A282511 * A282513 A282514 A282515

KEYWORD

nonn,frac

AUTHOR

Ralf Steiner, Feb 17 2017

EXTENSIONS

Corrected by Robert Israel, May 01 2017

STATUS

approved

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Last modified October 19 15:39 EDT 2018. Contains 316365 sequences. (Running on oeis4.)