A179273 Primes in A179272.

2, 5, 7, 11, 19, 23, 29, 41, 47, 71, 79, 89, 109, 131, 167, 181, 223, 239, 271, 359, 379, 419, 439, 461, 599, 701, 727, 811, 839, 929, 991, 1087, 1223, 1259, 1367, 1481, 1559, 1721, 1847, 1979, 2069, 2161, 2207, 2351, 2399, 2549, 2861, 2969, 3023, 3079, 3191

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

Cf. A000040, A179272.

Sequence in context: A162491 A152216 A045350 * A251964 A045351 A051645

Adjacent sequences: A179270 A179271 A179272 * A179274 A179275 A179276

Keyword

easy,nonn

Author

Jonathan Vos Post, Jul 07 2010

Extensions

More terms from R. J. Mathar, Oct 15 2010

Status

approved