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

Author

Amarnath Murthy, Sep 10 2003

Keywords

• nonn

Examples

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

Links

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

Programs

Magma

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

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 *)

Formula

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

Extensions

More terms from David Wasserman, Jun 01 2005

Edited by Robert Israel, Dec 23 2018