This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A085520 #12 May 25 2024 17:52:30
%S A085520 12,13,15,17,20,21,24,26,28,29,30,31,34,36,38,39,42,43,45,47,50,51,54,
%T A085520 56,58,59,62,63,65,67,70,71,74,76,78,79,82,83,85,87,92,93,95,97,120,
%U A085520 121,124,126,128,129,130,131,134,136,138,139
%N A085520 Numbers whose digits alternate between prime and nonprime.
%H A085520 Harvey P. Dale, <a href="/A085520/b085520.txt">Table of n, a(n) for n = 1..1000</a>
%e A085520 151 is in the sequence as 1 is nonprime and 5 is prime.
%t A085520 dapnQ[n_]:=Module[{c=Boole[PrimeQ[IntegerDigits[n]]],len},len=Length[c];c==PadRight[{},len,{0,1}]||c==PadRight[{},len,{1,0}]]; Select[ Range[ 10,200],dapnQ] (* _Harvey P. Dale_, Jul 21 2019 *)
%K A085520 nonn,base
%O A085520 1,1
%A A085520 Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 02 2003
%E A085520 Corrected (120 inserted) by _Harvey P. Dale_, Jul 21 2019