A260384 - OEIS

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 n-th primorial.

6, 16, 44, 122, 268, 556, 886, 1446, 1964, 2900

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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, pn-1, if (isprime(2*pn-p), v = concat(v, p))); my(w = vector(#v-1, 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(P-p), r=max(r, p-last); last=p)); r \\ Charles R Greathouse IV, Jul 24 2015

CROSSREFS

Cf. A002110.

Sequence in context: A317758 A010915 A352115 * A126360 A264545 A296855

Adjacent sequences: A260381 A260382 A260383 * A260385 A260386 A260387

KEYWORD

nonn,more

AUTHOR

Jean-Marc 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