OFFSET

1,1

LINKS

N. Makarova and others, Distributed computing project, discussion at the scientific forum dxdy.ru (in Russian), Feb. 2015.

FORMULA

a(n) = A000040(k), where k = least number such that A359440(k+n-1) >= n-1. - Peter Munn, Jan 05 2023

EXAMPLE

The first term is 2 since the 2 primes 2, 3 have a gap of 1, which is trivially symmetric about its center.

The second term is 5 since the 4 primes 5, 7, 11, 13 have gaps 2, 4, 2, which is symmetric about its center.

The twelve primes 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193 have gaps 2, 10, 2, 6, 6, 4, 6, 6, 2, 10, 2 - symmetric about the middle, so a(6) = 137.

PROG

(PARI) A081235(n) = { my(last=vector(n*=2, i, prime(i)), m, i=Mod(n-2, n)); forprime(p=last[n], default(primelimit), m=last[1+lift(i+2)]+last[1+lift(i++)]=p; for(j=1, n\2, last[1+lift(i-j)]+last[1+lift(i+j+1)]==m||next(2)); return(last[1+lift(i+1)]))} \\ M. F. Hasler, Apr 02 2010

CROSSREFS

KEYWORD

more,nonn

AUTHOR

Christopher Hunt Gribble and T. D. Noe, Apr 02 2010

EXTENSIONS

a(11) from Dmitry Petukhov, added by Max Alekseyev, Aug 08 2014

a(12) from an anonymous participant of the project, added by Natalia Makarova, Jul 16 2015

STATUS

approved