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 A367349 #8 Nov 18 2023 11:53:48 %S A367349 4,10,15,20,24,30,40,44,50,60,64,65,70,80,84,90 %N A367349 List of numbers in the range 1 to 99 missing from A366487. %C A367349 These numbers do not occur as differences between successive terms in A121805. %H A367349 Carlos Rivera, <a href="https://www.primepuzzles.net/puzzles/puzz_980.htm">Puzzle 980. The "Commas" sequence</a>, The Prime Puzzles and Problems Connection. %t A367349 a[1] = 1; a[n_] := a[n] = For[r = Mod[a[n - 1], 10]; y = 0, y <= 9, y++, If[y == IntegerDigits[#][[1]], Return[#]] &[a[n - 1] + 10 r + y]]; Complement[Range[99], Union@ Differences@ Array[a, 10^6]] (* _Michael De Vlieger_, Nov 18 2023, after _Jean-François Alcover_ at A121805 *) %Y A367349 Cf. A121805, A366487. %K A367349 nonn,base,fini,full %O A367349 1,1 %A A367349 _N. J. A. Sloane_, Nov 17 2023