A090869 - OEIS

%I #32 Jul 02 2024 07:18:38

%S 613,877,1117,1721,1753,2153,2557,2671,4349,4943,5039,5179,5443,5641,

%T 5939,6037,6827,6997,7591,7853,8069,8209,8527,8669,9221,9311,9377,

%U 9859,10729,11149,11353,11503,11933,12211,12413,12743,12923,13001,13037,13367,13693,13729,13999,14369,14449,14551,14759,15541,15923,16141

%N Irregular primes whose indices are irregular primes of order one.

%C This sequence is infinite.

%H Amiram Eldar, <a href="/A090869/b090869.txt">Table of n, a(n) for n = 1..10000</a>

%H Cino Hilliard, <a href="/A090869/a090869.txt">file irregprimes.txt</a>, Feb 13, 2004. [cached from Yahoo group B2LCC/files/Bernoulli/]

%H Mohammad Amin Shokrollahi, <a href="http://algo.epfl.ch/~amin/TAB.html">Tables</a>.

%F a(n) = A000928(A000928(n)). - _Amiram Eldar_, Jul 02 2024

%e 37 is the first irregular prime, 613 is the 37th irregular prime, i.e., iprime(iprime(1)) = 613, so a(1) = 613.

%o (PARI) \\ Irregular prime-indexed primes. Download the linked file (e.g. with "wget https://oeis.org/a090869.txt") into the gp working directory, and start a new PARI session.

%o iprime = readvec("your_path/a090869.txt");

%o ipips(n) = for(x=1, n, y=iprime[iprime[x]]; print1(y ", "));

%o ipips(50) \\ _Michel Marcus_, _Georg Fischer_ Nov 14 2019

%Y Cf. A000928 (irregular primes).

%K easy,nonn

%O 1,1

%A _Cino Hilliard_, Feb 12 2004