A080697 a(n) = n * prime(prime(n)).

3, 10, 33, 68, 155, 246, 413, 536, 747, 1090, 1397, 1884, 2327, 2674, 3165, 3856, 4709, 5094, 6289, 7060, 7707, 8822, 9913, 11064, 12725, 14222, 15201, 16436, 17371, 18510, 21979, 23648, 25509, 27098, 30065, 31572, 34003, 36746, 38649, 41240

Offset: 1

Author

Cino Hilliard, Mar 04 2003

Keywords

• nonn
• easy

Comments

Previous name was: "Product of prime-index-primes and the index of their prime index".

Sum of reciprocals converges to about 1/2. [More accurately, 0.50056748... . - Amiram Eldar, Jul 13 2024]

Examples

			a(1) = 1*prime(prime(1)) = 1*prime(2) = 1*3 = 3.
a(2) = 2*prime(prime(2)) = 2*prime(3) = 2*5 = 10.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A006450, A033286.

Programs

Magma

[n*NthPrime(NthPrime(n)): n in [1..40]]; // Vincenzo Librandi, Jun 09 2016

Mathematica

Table[n Prime[Prime[n]], {n, 1, 40}] (* Vincenzo Librandi, Jun 09 2016 *)

PARI

pipxindex(n) = {sr=0; pr=1; for(x=1,n, y=prime(prime(x)); pr=x*y; print1(pr" "); sr+=1.0/pr; ); print(); print(sr) }

Formula

a(n) = n*A006450(n). - Omar E. Pol, Oct 21 2013

Extensions

New name from Omar E. Pol, Oct 21 2013