A392050 a(n) is the denominator of the harmonic mean of the digits of n.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 2, 5, 3, 7, 4, 9, 5, 1, 3, 1, 5, 3, 7, 1, 9, 5, 11, 1, 2, 5, 1, 7, 4, 1, 5, 11, 2, 1, 5, 3, 7, 1, 9, 5, 11, 3, 13, 1, 3, 7, 4, 9, 1, 11, 6, 13, 7, 1, 7, 1, 1, 5, 11, 1, 13, 7, 5, 1, 4, 9, 5, 11, 6, 13, 1, 15, 8, 1, 9, 5, 11, 3, 13, 7, 15, 1, 17

Offset

0,13

Links

Table of n, a(n) for n=0..89.

Eric Weisstein's World of Mathematics, Harmonic Mean.

Wikipedia, Harmonic mean.

Formula

a(A011540(n)) = 1.

a(A392051(n)) = 1.

Example

a(43) = denominator(2*4*3/(4 + 3)) = denominator(24/7) = 7.

Mathematica

a[n_]:=Denominator[HarmonicMean[IntegerDigits[n]]]; Array[a, 90, 0]

Prog

(Python)
from fractions import Fraction
def a(n):
    d = list(map(int, str(n)))
    return 1 if 0 in d else (len(d)/sum(Fraction(1, di) for di in d)).denominator
print([a(n) for n in range(90)]) # Michael S. Branicky, Dec 29 2025

Crossrefs

Cf. A011540, A371384, A392049 (numerator), A392051.

Sequence in context: A076605 A367727 A318516 * A367728 A194748 A323462

Adjacent sequences: A392047 A392048 A392049 * A392051 A392052 A392053

Keyword

nonn,base,easy,frac

Author

Stefano Spezia, Dec 29 2025

Status

approved