A144519 Triangular numbers n*(n+1)/2 with n prime and n+1 nonprime.

6, 15, 28, 66, 91, 153, 190, 276, 435, 496, 703, 861, 946, 1128, 1431, 1770, 1891, 2278, 2556, 2701, 3160, 3486, 4005, 4753, 5151, 5356, 5778, 5995, 6441, 8128, 8646, 9453, 9730, 11175, 11476, 12403, 13366, 14028, 15051, 16110, 16471, 18336, 18721, 19503, 19900, 22366, 24976, 25878

Offset

1,1

Comments

This is A034953 without the 3. [From R. J. Mathar, Feb 21 2009]

Links

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

Example

If n=3(prime) and n=4(nonprime), then 3*4/2=6=a(1). If n=5(prime) and n=6(nonprime), then 5*6/2=15=a(2). If n=7(prime) and n=8(nonprime), then 7*8/2=28=a(3). If n=11(prime) and n=12(nonprime), then 11*12/2=66=a(4). If n=13(prime) and n=14(nonprime), then 13+14/2=91=a(5), etc.

Mathematica

Table[(p(p+1))/2, {p, Prime[Range[2, 50]]}] (* Harvey P. Dale, Dec 28 2023 *)

Crossrefs

Cf. A000040, A000217, A141468, A144291.

Sequence in context: A115742 A026102 A338024 * A066995 A263896 A295979

Adjacent sequences: A144516 A144517 A144518 * A144520 A144521 A144522

Keyword

nonn

Author

Juri-Stepan Gerasimov, Dec 15 2008

Extensions

Corrected definition. Inserted 2701, extended beyond 11175. - R. J. Mathar, Dec 19 2008

Status

approved