A192394 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A192394

Number of semiprimes in the range (prime(n), prime(n)+sqrt(prime(n))).

0, 1, 1, 1, 1, 2, 1, 2, 2, 2, 3, 2, 1, 2, 2, 3, 2, 2, 2, 2, 2, 4, 4, 4, 1, 2, 2, 2, 4, 6, 3, 4, 5, 5, 4, 4, 5, 2, 3, 4, 3, 4, 4, 6, 6, 7, 7, 3, 2, 2, 3, 4, 4, 5, 4, 4, 2, 3, 4, 4, 6, 8, 5, 6, 7, 7, 5, 4, 5, 5, 6, 5, 5, 5, 8

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

LINKS

Table of n, a(n) for n=1..75.

EXAMPLE

a(1)=0 because there are no semiprimes in the range (2, 2+sqrt(2));

a(2)=1 because there is one semiprime (4) in the range (3, 3+sqrt(3)).

MAPLE

A192394 := proc(n) local a, p, s; a := 0 ; p := ithprime(n) ; for s from p to floor( p+sqrt(p)) do if isA001358(s) then a := a+1 ; end if; end do: a; end proc: # R. J. Mathar, Jul 01 2011

MATHEMATICA

(* First run A072000 to define semiPrimePi *) Table[semiPrimePi[Prime[n] + Sqrt[Prime[n]]] - semiPrimePi[Prime[n]], {n, 75}] (* Alonso del Arte, Jul 01 2011 *)

CROSSREFS

Cf. A001358.

Sequence in context: A024936 A144590 A057368 * A085033 A230254 A299484

Adjacent sequences: A192391 A192392 A192393 * A192395 A192396 A192397

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jun 29 2011

EXTENSIONS

Corrected by R. J. Mathar, Jul 01 2011

STATUS

approved