OFFSET
1,1
LINKS
R. Zumkeller, Table of n, a(n) for n = 1..10000
EXAMPLE
MATHEMATICA
a[n_] := PrimePi[Prime[n] + n] - PrimePi[Prime[n] - n - 1];
Array[a, 100] (* Jean-François Alcover, Jun 11 2019 *)
PROG
(Sage)
[len([k for k in (nth_prime(n)-n..nth_prime(n)+n) if is_prime(k)]) for n in (1..75)] # Peter Luschny, Sep 03 2013
(PARI) a(n) = my(p=prime(n)); primepi(p+n) - primepi(p-n-1); \\ Michel Marcus, Jun 11 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 05 2004
STATUS
approved