A039145 Numbers whose base-10 representation has the same number of 4's and 9's.

0, 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 15, 16, 17, 18, 20, 21, 22, 23, 25, 26, 27, 28, 30, 31, 32, 33, 35, 36, 37, 38, 49, 50, 51, 52, 53, 55, 56, 57, 58, 60, 61, 62, 63, 65, 66, 67, 68, 70, 71, 72, 73, 75, 76, 77, 78, 80, 81, 82, 83, 85, 86, 87, 88, 94, 100, 101, 102

Offset

1,3

Links

Table of n, a(n) for n=1..69.

Mathematica

Select[Range[0, 200], DigitCount[#, 10, 4] == DigitCount[#, 10, 9] &] (* Vincenzo Librandi, Oct 27 2016 *)

Prog

(Magma) [n: n in [0..120] | Multiplicity(S, 4) eq Multiplicity(S, 9) where S is {*d: d in Intseq(n)*}]; // Vincenzo Librandi, Oct 27 2016
(Python)
from itertools import count, islice
def A039145_gen(startvalue=0): # generator of terms >= startvalue
    return filter(lambda k:(s:=str(k)).count('4')==s.count('9'), count(max(startvalue, 0)))
A039145_list = list(islice(A039145_gen(), 40)) # Chai Wah Wu, Mar 05 2024

Crossrefs

Sequence in context: A138309 A184514 A001068 * A242491 A038129 A062071

Adjacent sequences: A039142 A039143 A039144 * A039146 A039147 A039148

Keyword

nonn,base,easy

Author

Olivier Gérard

Status

approved