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Terms as well as digits have alternating primality; this is the lexicographically earliest injective sequence with this property.
4

%I #19 Jan 02 2023 12:30:49

%S 1,2,4,3,6,5,8,7,9,29,20,31,21,59,24,71,26,79,28,263,12,13,15,17,42,

%T 43,45,47,62,67,63,83,65,97,82,131,30,283,85,139,34,293,87,151,36,307,

%U 92,179,38,313,93,421,39,317,95,431,50,347,120,367,121,383,124,397,126,503,128,547,129,563,130,587,134,593,136,743,138,787

%N Terms as well as digits have alternating primality; this is the lexicographically earliest injective sequence with this property.

%C Exactly every other term, and also every other digit (in concatenated terms) is prime.

%H Carole Dubois, <a href="/A217560/b217560.txt">Table of n, a(n) for n = 1..5292</a>

%H E. Angelini, <a href="http://list.seqfan.eu/oldermail/seqfan/2012-October/010253.html">Non-primes/primes: integers and digits alternate</a>, SeqFan mailing list, Oct 06 2012

%H Carole Dubois, <a href="/A217560/a217560.jpg">Graph with even ranges and odd ranges separated</a>

%Y The sequence A217559 is a simplified variant.

%Y See also A217555, A217556, where "primality" is replaced by "parity".

%K nonn,base

%O 1,2

%A _Eric Angelini_ and _M. F. Hasler_, Oct 06 2012

%E Values from a(26)=43 on corrected by _Jean-Marc Falcoz_, Oct 10 2012