A171574 Primes of the form floor(binomial(k,2)/4).

2, 3, 5, 7, 11, 13, 19, 47, 101, 157, 331, 457, 569, 1069, 1237, 1471, 1667, 2161, 2467, 2719, 3061, 3719, 4027, 4441, 5227, 5591, 6469, 6991, 7411, 9011, 11287, 14407, 15797, 16607, 18097, 21269, 21997, 24697, 29221, 30319, 32321, 35311, 38711

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

floor(10/4)=2, floor(15/4)=3, floor(21/4)=5, ...

Mathematica

f[n_]:=n*(n+1)/2; lst={}; Do[If[PrimeQ[p=Floor[f[n]/4]], AppendTo[lst, p]], {n, 7!}]; lst
Select[Floor[Accumulate[Range[600]]/4], PrimeQ] (* Harvey P. Dale, Nov 09 2022 *)

Crossrefs

Cf. A000217.

Sequence in context: A362850 A338396 A067910 * A354800 A280937 A296236

Adjacent sequences: A171571 A171572 A171573 * A171575 A171576 A171577

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Dec 12 2009

Status

approved