OFFSET
1,1
COMMENTS
Primes of form floor(((n^2)/4) - (n/2) - 1). Primes in sharp upper bound on Rosgen overlap number n-vertex graph with n => 14, formula abused here for nonnegative integers. There seem to be more primes (29) through n = 60 of floor(((n^2)/4) - (n/2) - 1) than one might expect. What fraction through n = 1000 are prime?
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
Daniel W. Cranston, Nitish Korula, Timothy D. LeSaulnier, Kevin Milans, Christopher Stocker, Jennifer Vandenbussche, Douglas B. West, Overlap Number of Graphs, Jul 06, 2010.
EXAMPLE
a(1) = floor(((5^2)/4) - (5/2) - 1) = floor(16/4 - 5/2 - 1) = floor(11/4) = 2.
a(2) = floor(((6^2)/4) - (6/2) - 1) = floor(36/4 - 6/2 - 1) = floor(5) = 5.
MATHEMATICA
Select[Table[Floor[n^2/4-n/2-1], {n, 5, 200}], PrimeQ] (* Harvey P. Dale, Oct 12 2012 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Jul 07 2010
EXTENSIONS
More terms from R. J. Mathar, Oct 15 2010
STATUS
approved