A115887 - OEIS

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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

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OFFSET

1,2

LINKS

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

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

Cf. A115883.

Sequence in context: A110891 A197435 A240514 * A068195 A080506 A109163

Adjacent sequences: A115884 A115885 A115886 * A115888 A115889 A115890

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 06 2006

STATUS

approved