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%I #11 Sep 08 2022 08:45:08
%S 7,11,17,29,43,67,97,131,173,227,277,349,421,499,599,683,809,919,1039,
%T 1181,1307,1483,1621,1811,2003,2207,2389,2633,2819,3067,3329,3571,
%U 3833,4099,4397,4691,5003,5347,5657,6007,6329,6703,7057,7499,7873,8287,8707,9133
%N a(n) = prime(n*(n+1)/2+4).
%C More generally one may consider the sequence S(n, m) = prime(n*(n+1)/2+m+1), for m=1, 2, 3...
%H Vincenzo Librandi, <a href="/A078725/b078725.txt">Table of n, a(n) for n = 0..1000</a>
%t Table[Prime[(n (n + 1))/2 + 4], {n, 0, 60}] (* _Vincenzo Librandi_, Jun 08 2016 *)
%o (PARI) triprimes(n,m) = { sr = 0; for(j=m,n, x = j*(j+1)/2+m+1; z = prime(x); sr+=1.0/z; print1(z" "); ); print(); print(sr); }
%o (Magma) [NthPrime(n*(n+1) div 2 + 4): n in [0..50]]; // _Vincenzo Librandi_, Jun 08 2016
%Y Apart from initial terms, primes in fourth diagonal of triangle in A078721.
%K nonn,easy
%O 0,1
%A _Cino Hilliard_, Dec 20 2002