OFFSET
1,7
EXAMPLE
If n < 6, then in every arrangement of the numbers 1 through n on a circle, there are two adjacent numbers adding up to a prime. For n = 6, the only arrangement without a prime sum is (1, 3, 6, 2, 4, 5).
CROSSREFS
KEYWORD
nonn
AUTHOR
Jens Voß, May 04 2012
EXTENSIONS
a(15)-a(17) from Alois P. Heinz, May 04 2012
a(18) from R. H. Hardin, May 07 2012
a(19)-a(30) from Max Alekseyev, Aug 19 2013
STATUS
approved