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 A375214 #16 Sep 13 2024 07:41:04 %S A375214 21,23,25,27,29,41,43,45,47,49,61,63,65,67,69,81,83,85,87,89,1001, %T A375214 1003,1005,1007,1009,1021,1023,1025,1027,1029,1041,1043,1045,1047, %U A375214 1049,1061,1063,1065,1067,1069,1081,1083,1085,1087,1089,1201,1203,1205,1207,1209,1221,1223,1225 %N A375214 Odd numbers with equal numbers of even and odd digits. %C A375214 Numbers with an odd length cannot be in this sequence. %H A375214 Jake L Lande, <a href="/A375214/b375214.txt">Table of n, a(n) for n = 1..1000</a> %e A375214 1001 is odd and has two even digits (0,0) and two odd digits (1,1). %p A375214 filter:= proc(n) local L; %p A375214 L:= convert(n,base,10); %p A375214 nops(select(type,L,even))=nops(L)/2 %p A375214 end proc: %p A375214 select(filter, [seq(seq(i,i=10^(d-1)+1 .. 10^d, 2),d=2..4,2)]); # _Robert Israel_, Aug 07 2024 %t A375214 eeo[n_] := (id = IntegerDigits[n]; Count[EvenQ@id, True] == Count[OddQ@id, True]); Select[Select[Range[1225], eeo], Mod[#, 2] == 1 &] %Y A375214 Subsequence of A227870. %Y A375214 Complement of A375213 within A227870. %K A375214 nonn,base,easy %O A375214 1,1 %A A375214 _Jake L Lande_, Aug 07 2024