A192394 - OEIS

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

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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