A391869 Delete from n all digits of opposite parity to its largest digit.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 11, 2, 13, 4, 15, 6, 17, 8, 19, 20, 2, 22, 3, 24, 5, 26, 7, 28, 9, 3, 31, 3, 33, 4, 35, 6, 37, 8, 39, 40, 4, 42, 4, 44, 5, 46, 7, 48, 9, 5, 51, 5, 53, 5, 55, 6, 57, 8, 59, 60, 6, 62, 6, 64, 6, 66, 7, 68, 9, 7, 71, 7, 73, 7, 75

Offset

0,3

Comments

Look at the largest digit of n. If it is even, remove all odd digits of n. If it is odd, remove all even digits. The remaining digits form the term.

Links

Michael S. Branicky, Table of n, a(n) for n = 0..10000

Formula

a(k) = k for k in A059708.

Example

a(1121) = 2 since the largest digit is 2, and we delete the odd 1 digits to obtain 2.
a(3674) = 37 since the largest digit is 7, and we delete the even digits 6 and 4 to obtain 37.
a(5060) = 60 since the largest digit is 6, and we delete the odd 5 digit to obtain (0)60.

Mathematica

a[n_] := Module[{d = IntegerDigits[n]}, FromDigits@ DeleteCases[d, _?(Mod[#, 2] != Mod[Max[d], 2] &)]]; Array[a, 100, 0] (* Amiram Eldar, Jan 19 2026 *)

Prog

(Python)
def a(n):
    s = str(n)
    dmax = max(s)
    digset = "02468" if (dmax in "13579") else "13579"
    r = "".join(d for d in s if d not in digset)
    return int(r)
print([a(n) for n in range(76)])
(PARI) a(n) = if (n, my(d=digits(n), p=vecmax(d) % 2, list=List()); for (i=1, #d, if ((d[i] % 2) == p, listput(list, d[i]))); fromdigits(Vec(list)), 0); \\ Michel Marcus, Jan 19 2026

Crossrefs

Cf. A059708 (set of fixed points).

Sequence in context: A344487 A389420 A047813 * A084051 A069652 A055483

Adjacent sequences: A391866 A391867 A391868 * A391870 A391871 A391872

Keyword

nonn,base,easy

Author

Ali Sada and Michael S. Branicky, Jan 18 2026

Status

approved