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A166678 Pi[(sqrt[ p_k!! ] +1)^2] -Pi [p_k!! ], where Pi(n) = number of primes <=n; P!! = 2*3*5*7*...*p ; p_k is k-th prime. 0
2, 2, 3, 6, 14, 34, 110, 384, 1540, 7019, 34501, 183439, 1045196, 6164423, 38285946 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: k <= Pi((Sqrt[p_k!! ]+1)^2) - Pi(p_k!!)

LINKS

Table of n, a(n) for n=1..15.

MATHEMATICA

a[n_] := Product[Prime[k], {k, 1, n}]; Table[PrimePi[(Sqrt[a[n]] + 1)^2] - PrimePi[a[n]], {n, 1, 12}] (* G. C. Greubel, May 22 2016 *)

CROSSREFS

Sequence in context: A064674 A095902 A103687 * A032908 A192366 A318039

Adjacent sequences:  A166675 A166676 A166677 * A166679 A166680 A166681

KEYWORD

nonn

AUTHOR

Daniel Tisdale, Oct 18 2009, Oct 23 2009

EXTENSIONS

a(13)-a(15) from Ray Chandler, May 10 2010

STATUS

approved

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Last modified August 25 02:56 EDT 2019. Contains 326318 sequences. (Running on oeis4.)