This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A087397 #14 Jan 01 2024 13:09:09
%S A087397 3,10,6,15,45,66,120,153,231,378,435,630,780,861,1035,1326,1653,1770,
%T A087397 2145,2415,2556,3003,3321,3828,4560,4950,5151,5565,5778,6216,7875,
%U A087397 8385,9180,9453,10878,11175,12090,13041,13695,14706,15753,16110,17955,18336
%N A087397 Smallest triangular number > 1 and == 1 (mod prime(n)).
%H A087397 Robert Israel, <a href="/A087397/b087397.txt">Table of n, a(n) for n = 1..10000</a>
%F A087397 a(n) = (prime(n)-2)*(prime(n)-1)/2 for n >= 3.
%e A087397 a(7) = 120 == 1 (mod 17), prime (7) = 17.
%p A087397 3,10, seq((ithprime(i)-2)*(ithprime(i)-1)/2, i=3..50); # _Robert Israel_, Dec 23 2018
%t A087397 Join[{3, 10}, Table[(Prime[n] - 2) (Prime[n] - 1) / 2, {n, 3, 50}]] (* _Vincenzo Librandi_, Dec 24 2018 *)
%o A087397 (Magma) [3,10] cat [(NthPrime(n)-2)*(NthPrime(n)-1)/2: n in [3..50]]; // _Vincenzo Librandi_, Dec 24 2018
%K A087397 nonn
%O A087397 1,1
%A A087397 _Amarnath Murthy_, Sep 10 2003
%E A087397 More terms from _David Wasserman_, Jun 01 2005
%E A087397 Edited by _Robert Israel_, Dec 23 2018