cp's OEIS Frontend

A303847 Lexicographically earliest sequence of distinct terms such that what emerges from the mask (right-aligned) is prime (see the Comments section for the mask explanation).

%I A303847 #9 May 02 2018 09:26:06
%S A303847 1,20,2,21,3,22,4,23,5,24,6,25,7,26,8,27,9,28,200,10,201,11,202,12,
%T A303847 203,13,204,14,205,15,206,16,207,17,208,18,209,19,210,29,211,30,212,
%U A303847 31,213,32,214,33,215,34,216,35,217,36,218,37,219,38,220,39,221,40,222,41,223,42,224,43,225,44,226,45,227,46,228,47
%N A303847 Lexicographically earliest sequence of distinct terms such that what emerges from the mask (right-aligned) is prime (see the Comments section for the mask explanation).
%C A303847 For any pair of consecutive terms, one of the terms uses fewer digits than the other. This term is called the mask. Put the mask on the other term, starting from the right. What is not covered by the mask forms a prime number on the left.
%C A303847 The sequence starts with a(1) = 1 and is always extended with the smallest integer not yet present that doesn't lead to a contradiction.
%C A303847 This sequence is a permutation of the positive integers, as all integers will appear at some point, either as mask or masked.
%H A303847 Jean-Marc Falcoz, <a href="/A303847/b303847.txt">Table of n, a(n) for n = 1..10001</a>
%e A303847 In the pair (1,20), 1 is the mask; 2 emerges and is prime;
%e A303847 in the pair (20,2), 2 is the mask; 2 emerges and is prime;
%e A303847 in the pair (2,21), 2 is the mask; 2 emerges and is prime;
%e A303847 in the pair (21,3), 3 is the mask; 2 emerges and is prime;
%e A303847 ...
%e A303847 in the pair (117,2018), 117 is the mask; 2 emerges and is prime;
%e A303847 etc.
%Y A303847 Cf. A303782 (same idea, but the mask is left-aligned).
%K A303847 nonn,base
%O A303847 1,2
%A A303847 _Eric Angelini_ and _Jean-Marc Falcoz_, May 01 2018