A190303 - OEIS

A190303

Decimal expansion of sum of alternating series of reciprocals of Ramanujan primes, Sum_{n>=1} (1/R_n)(-1)^(n-1), where R_n is the n-th Ramanujan prime, A104272(n).

4, 4, 6, 6, 8, 4, 3, 0, 7

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OFFSET

0,1

COMMENTS

Computed 0.446684 for n = 1 to 65536, using Open Office Calc. Next digit expected to be between 2 and 3.

By computing all Ramanujan primes less than 10^9, we find that about 9 decimal places of the sum should be correct: 0.446684307 (truncated, not rounded). The following table shows the number of Ramanujan primes between powers of 10 and the sum of the alternating reciprocals of those primes.

1 1 0.50000000000000000

2 9 -0.05765566386047510

3 62 0.00388002010130731

4 487 0.00050881775862179

5 3900 -0.00004384563815649

6 32501 -0.00000552572415587

7 279106 0.00000045427780897

8 2444255 0.00000005495474474

9 21731345 -0.00000000549864067

Total: 0.44668430669928564 - T. D. Noe, May 08 2011

Let E_n denote the error after the first n terms in the series. Then by the Alternating Series Test, 1/R_{n+1} - 1/R_{n+2} < E_n < 1/R_{n+1}. [Jonathan Sondow, May 10 2011]

LINKS

Table of n, a(n) for n=0..8.

J. Sondow, Ramanujan primes and Bertrand's postulate, arXiv:0907.5232 [math.NT], 2009-2010.

J. Sondow, Ramanujan primes and Bertrand's postulate, Amer. Math. Monthly 116 (2009), 630-635.

J. Sondow, J. W. Nicholson, and T. D. Noe, Ramanujan Primes: Bounds, Runs, Twins, and Gaps, J. Integer Seq. 14 (2011) Article 11.6.2

Eric W. Weisstein, Prime Sums

FORMULA

Sum_{n>=1} (-1)^(n-1)(1/R_n), where R_n is the n-th Ramanujan prime, A104272(n).

EXAMPLE

0.446684307...

CROSSREFS

Cf. A104272, A085548, A078437, A190124.

Sequence in context: A111657 A049751 A196594 * A175123 A276679 A163638

Adjacent sequences: A190300 A190301 A190302 * A190304 A190305 A190306

KEYWORD

nonn,cons,more

AUTHOR

John W. Nicholson, May 07 2011

EXTENSIONS

Definition corrected by Jonathan Sondow, May 10 2011

STATUS

approved