cp's OEIS Frontend

A268031 Primes with the property that deleting some two digits one at a time in unique order gives a prime (with an even number of digits) at each step, until the empty string is reached.

%I A268031 #11 Apr 03 2023 10:36:13
%S A268031 11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,1009,
%T A268031 1021,1049,1051,1063,1069,1087,1201,1409,1609,1663,1669,1801,2003,
%U A268031 2011,2017,2063,2069,2267,2609,2621,2657,2663,2687,2767,2861,3001,3023
%N A268031 Primes with the property that deleting some two digits one at a time in unique order gives a prime (with an even number of digits) at each step, until the empty string is reached.
%H A268031 Chris Caldwell, The Prime Glossary, <a href="https://t5k.org/glossary/xpage/DeletablePrime.html">Deletable prime</a>
%e A268031 The prime 2657 is in the sequence because the set {57, 67, 65, 27, 25, 26} contains only one two-digit prime.
%e A268031 The prime 1021 is in the sequence because the set {21, 1, 2, 11, 12, 10} contains only one prime with an even number of digits.
%e A268031 The prime 1579 is not in the sequence because the set {79, 59, 57, 19, 17, 15} contains four two-digit primes.
%e A268031 The number 2087 is not in the sequence because the set {87, 7, 8, 27, 28, 20} does not contain any prime with an even number of digits.
%o A268031 (Magma) /* generates first 211 terms */; lst:=[m: m in [11..99 by 2] | IsPrime(m)]; for m in [1001..9999 by 2] do if IsPrime(m) then S:=[]; Temp:=Intseq(m); for a in [2..4] do for b in [1..a-1] do d:=Seqint([Temp[b], Temp[a]]); if IsPrime(d) and d gt 10 then Append(~S, d); end if; end for; end for; if #S eq 1 then Append(~lst, m); end if; end if; end for; lst; // _Arkadiusz Wesolowski_, Dec 17 2020
%Y A268031 Cf. A080608, A188809.
%K A268031 nonn,base
%O A268031 1,1
%A A268031 _Arkadiusz Wesolowski_, Jan 24 2016