A309572 - OEIS

%I #23 Aug 11 2019 01:45:26

%S 0,1,3,5,5,7,19,7,9,6,25,11,22,16,18,12,54,12,48,18,33,13,103,16,27,

%T 20,50,13,161,14,66,27,47,19,109,18,67,22,70,15,226,22,82,33,67,24,

%U 261,26,137,29,89,23,273,29,102,31,82,24,546,26,119,37,110,29

%N Number of primes of which all substrings in base n are primes.

%H Rémy Sigrist, <a href="/A309572/b309572.txt">Table of n, a(n) for n = 2..2500</a> (first 199 terms from Lucas H. Gabrielli)

%H Rémy Sigrist, <a href="/A309572/a309572.png">Colored logarithmic scatterplot of the first 2500 terms</a>

%H Rémy Sigrist, <a href="/A309572/a309572.gp.txt">PARI program for A309572</a>

%e For base 10, there are 9 primes whose substrings are also primes: 2, 3, 5, 7, 23, 37, 53, 73, and 373, thus a(10) = 9.

%o (PARI) See Links section.

%Y Cf. A245277.

%K base,nonn

%O 2,3

%A _Lucas H. Gabrielli_, Aug 08 2019