cp's OEIS Frontend

A363572 Lexicographically earliest sequence of distinct terms > 0 such that the concatenation of the rightmost digit of a(n) and the leftmost digit of a(n+1) forms a prime number. The rightmost digit of a(n) cannot be 0.

%I A363572 #17 Mar 09 2024 08:19:09
%S A363572 1,3,7,9,71,11,12,31,13,14,15,32,33,16,17,18,34,19,72,35,36,73,74,37,
%T A363572 38,39,75,91,76,77,92,93,78,94,79,701,95,96,101,97,98,99,702,301,102,
%U A363572 302,303,103,104,105,304,106,107,108,305,306,109,703,111,112,307,113,114,115
%N A363572 Lexicographically earliest sequence of distinct terms > 0 such that the concatenation of the rightmost digit of a(n) and the leftmost digit of a(n+1) forms a prime number. The rightmost digit of a(n) cannot be 0.
%H A363572 Tyler Busby, <a href="/A363572/b363572.txt">Table of n, a(n) for n = 1..10000</a>
%H A363572 Eric Angelini, <a href="http://cinquantesignes.blogspot.com/2023/08/prime-welds.html">Prime welds</a>, Personal blog.
%e A363572 a(1) = 1 and a(2) = 3 form 13, a prime number;
%e A363572 a(2) = 3 and a(3) = 7 form 37, a prime number;
%e A363572 a(3) = 7 and a(4) = 9 form 79, a prime number;
%e A363572 a(4) = 9 and the leftmost digit of a(5) = 71 form 97, a prime number;
%e A363572 a(5) = 71 and its rightmost digit, concatenated to the leftmost digit of a(6) = 11, form 11, a prime number; etc.
%Y A363572 Cf. A152607.
%K A363572 base,nonn
%O A363572 1,2
%A A363572 _Eric Angelini_, Aug 17 2023