

A260384


Maximal gap between successive elements of Pn with n >= 3. Pn : primes p <= A002110(n) such that q=2*A002110(n)p is prime. (p, q) is a pair of centered primes at nth primorial.


1




OFFSET

3,1


LINKS

Table of n, a(n) for n=3..12.


EXAMPLE

For n=3, primorial(3)=A002110(3) is 30 and P3 is (7, 13, 17, 19, 23, 29) because (53, 47, 43, 41, 37, 31) are all prime. The maximum gap between two consecutive terms of P3 is 6, obtained for (7,13) or (23,29), so a(3)=6.


PROG

(PARI) lstp(n)=my(v = []); pn = prod(i=1, n, prime(i)); forprime(p=1, pn1, if (isprime(2*pnp), v = concat(v, p))); my(w = vector(#v1, k, v[k+1]  v[k])); vecmax(w); \\ Michel Marcus, Jul 24 2015
(PARI) a(n)=my(P=2*prod(i=1, n, prime(i)), r, last=P); forprime(p=2, P/2, if(isprime(Pp), r=max(r, plast); last=p)); r \\ Charles R Greathouse IV, Jul 24 2015


CROSSREFS

Cf. A002110.
Sequence in context: A107614 A317758 A010915 * A126360 A264545 A296855
Adjacent sequences: A260381 A260382 A260383 * A260385 A260386 A260387


KEYWORD

nonn,more


AUTHOR

JeanMarc Rebert, Jul 24 2015


EXTENSIONS

a(10) from Charles R Greathouse IV, Jul 24 2015
a(11) from Charles R Greathouse IV, Jul 28 2015
a(12) from Charles R Greathouse IV, Jul 30 2015


STATUS

approved



