OFFSET
1,4
COMMENTS
d(n) is the least d > 0 such that p, p+d, p+2d, ..., p+(p-1)d are all prime with p = p(n), and p(n-1)# = A002110(n-1) is a primorial.
d(n) is always a multiple of p(n-1)#.
a(5) and a(6) are due to G. Loh in 1986, and a(7) to Phil Carmody in 2001.
LINKS
EXAMPLE
Prime(3) = 5 and 5, 11, 17, 23, 29 is the smallest 5-term AP beginning with 5, so a(3) = (11-5)/p(2)# = 6/2*3 = 1.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Jonathan Sondow, Nov 08 2013
EXTENSIONS
a(8) due to Wojciech Izykowski in 2014 added by Jonathan Sondow, Aug 08 2019
STATUS
approved