A115887 Triangular numbers equal to the difference between a prime number and its index.

1, 3, 6, 10, 28, 105, 120, 153, 231, 465, 496, 1081, 1378, 1485, 1653, 1711, 2628, 3003, 3081, 3160, 4950, 5050, 5460, 6670, 6903, 8001, 8778, 10296, 11781, 14028, 15225, 16290, 19701, 20503, 21528, 21945, 22155, 24310, 24531, 25200, 27495

Offset: 1

Author

Giovanni Resta, Feb 06 2006

Keywords

• nonn

Examples

			28=T(7)=p(13)-13.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..500

Crossrefs

Cf. A115883.

Programs

Mathematica

Union[Select[Table[Prime[i]-i,{i,20000}],IntegerQ[Sqrt[8#+1]]&]] (* Harvey P. Dale, Jun 28 2012 *)