A356929 Integers with an even number of even digits.

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 20, 22, 24, 26, 28, 31, 33, 35, 37, 39, 40, 42, 44, 46, 48, 51, 53, 55, 57, 59, 60, 62, 64, 66, 68, 71, 73, 75, 77, 79, 80, 82, 84, 86, 88, 91, 93, 95, 97, 99, 100, 102, 104, 106, 108, 111, 113, 115, 117, 119, 120, 122, 124, 126, 128, 131, 133, 135

Offset

1,2

Comments

Inspired by Question 2 of Olympiade Mathématique Belge 2004, Finale MAXI (see link).

The number of n-digit integers with an even number of even digits is A137233(n).

Links

Table of n, a(n) for n=1..68.

Olympiade Mathématique Belge, OMB 2004, Finale Maxi, Question 2.

Index to sequences related to Olympiads.

Example

13 has zero even digit, so 13 is a term.
124 has two even digits, so 124 is a term.
3578 has one even digit, so 3578 is not a term.

Mathematica

Select[Range[120], EvenQ[Count[IntegerDigits[#], _?EvenQ]] &] (* Amiram Eldar, Sep 05 2022 *)

Prog

(Python)
def ok(n): return sum(1 for d in str(n) if d in "02468")%2 == 0
print([k for k in range(120) if ok(k)]) # Michael S. Branicky, Sep 05 2022
(PARI) isok(k) = (#select(x->(!(x % 2)), digits(k)) % 2) == 0; \\ Michel Marcus, Sep 06 2022

Crossrefs

Cf. A137233.

Sequence in context: A038124 A172273 A329835 * A187349 A238704 A338742

Adjacent sequences: A356926 A356927 A356928 * A356930 A356931 A356932

Keyword

nonn,base

Author

Bernard Schott, Sep 05 2022

Status

approved