A227870 Numbers with equal number of even and odd digits.

10, 12, 14, 16, 18, 21, 23, 25, 27, 29, 30, 32, 34, 36, 38, 41, 43, 45, 47, 49, 50, 52, 54, 56, 58, 61, 63, 65, 67, 69, 70, 72, 74, 76, 78, 81, 83, 85, 87, 89, 90, 92, 94, 96, 98, 1001, 1003, 1005, 1007, 1009, 1010, 1012, 1014, 1016, 1018, 1021, 1023, 1025

Offset: 1

Author

Jon Perry, Nov 02 2013

Keywords

• nonn
• base
• easy

Comments

Numbers with an odd digit length cannot be in this sequence. - Alonso del Arte, Nov 02 2013

Examples

			1009 has 2 even digits (00) and 2 odd digits (19) and so is in the sequence.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A001637.

Cf. A030141, A031443.

Programs

JavaScript

for (i = 1; i < 5000; i++) {
s = i.toString();
odds = 0; evens = 0;
for (j = 0; j < s.length; j++) if (s.charAt(j)%2 == 0) evens++; else odds++;
if (odds == evens) document.write(i + ", ");
}

Mathematica

Select[Range[1025], (d = Differences[Tally[Mod[IntegerDigits[#], 2]]]) != {} && d[[1, 2]] == 0 &] (* Amiram Eldar, Oct 01 2020 *)
eneodQ[n_]:=With[{id=IntegerDigits[n]},Count[id,?(OddQ[#]&)]==Count[id,?(EvenQ[#]&)]]; Select[Range[1100],eneodQ] (* Harvey P. Dale, Jul 19 2024 *)

PARI

isok(m) = my(d=digits(m)); #select(x->(x%2), d) == #select(x->!(x%2), d); \\ Michel Marcus, Oct 01 2020

Python

def ok(i):
  stri = str(i)
  se = sum(1 for d in stri if d in "02468")
  so = sum(1 for d in stri if d in "13579")
  return se == so
def aupto(nn):
  alst, an = [None], 0
  for n in range(1, nn+1):
    while len(alst) < nn+1:
      if ok(an): alst.append(an)
      an += 1
  return alst[1:] # use alst[n] for a(n)
print(aupto(58))  # Michael S. Branicky, Dec 14 2020