A078725 a(n) = prime(n*(n+1)/2+4).

7, 11, 17, 29, 43, 67, 97, 131, 173, 227, 277, 349, 421, 499, 599, 683, 809, 919, 1039, 1181, 1307, 1483, 1621, 1811, 2003, 2207, 2389, 2633, 2819, 3067, 3329, 3571, 3833, 4099, 4397, 4691, 5003, 5347, 5657, 6007, 6329, 6703, 7057, 7499, 7873, 8287, 8707, 9133

Offset: 0

Author

Cino Hilliard, Dec 20 2002

Keywords

• nonn
• easy

Comments

More generally one may consider the sequence S(n, m) = prime(n*(n+1)/2+m+1), for m=1, 2, 3...

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Crossrefs

Apart from initial terms, primes in fourth diagonal of triangle in A078721.

Programs

Magma

[NthPrime(n*(n+1) div 2 + 4): n in [0..50]]; // Vincenzo Librandi, Jun 08 2016

Mathematica

Table[Prime[(n (n + 1))/2 + 4], {n, 0, 60}] (* Vincenzo Librandi, Jun 08 2016 *)

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); }