A087397 Smallest triangular number > 1 and == 1 (mod prime(n)).

3, 10, 6, 15, 45, 66, 120, 153, 231, 378, 435, 630, 780, 861, 1035, 1326, 1653, 1770, 2145, 2415, 2556, 3003, 3321, 3828, 4560, 4950, 5151, 5565, 5778, 6216, 7875, 8385, 9180, 9453, 10878, 11175, 12090, 13041, 13695, 14706, 15753, 16110, 17955, 18336

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = (prime(n)-2)*(prime(n)-1)/2 for n >= 3.

Example

a(7) = 120 == 1 (mod 17), prime (7) = 17.

Maple

3, 10, seq((ithprime(i)-2)*(ithprime(i)-1)/2, i=3..50); # Robert Israel, Dec 23 2018

Mathematica

Join[{3, 10}, Table[(Prime[n] - 2) (Prime[n] - 1) / 2, {n, 3, 50}]] (* Vincenzo Librandi, Dec 24 2018 *)

Prog

(Magma) [3, 10] cat [(NthPrime(n)-2)*(NthPrime(n)-1)/2: n in [3..50]]; // Vincenzo Librandi, Dec 24 2018

Crossrefs

Sequence in context: A244846 A210415 A337275 * A210414 A289832 A196163

Adjacent sequences: A087394 A087395 A087396 * A087398 A087399 A087400

Keyword

nonn

Author

Amarnath Murthy, Sep 10 2003

Extensions

More terms from David Wasserman, Jun 01 2005

Edited by Robert Israel, Dec 23 2018

Status

approved