A392049 a(n) is the numerator of the harmonic mean of the digits of n.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 4, 3, 8, 5, 12, 7, 16, 9, 0, 4, 2, 12, 8, 20, 3, 28, 16, 36, 0, 3, 12, 3, 24, 15, 4, 21, 48, 9, 0, 8, 8, 24, 4, 40, 24, 56, 16, 72, 0, 5, 20, 15, 40, 5, 60, 35, 80, 45, 0, 12, 3, 4, 24, 60, 6, 84, 48, 36, 0, 7, 28, 21, 56, 35, 84, 7, 112, 63

Offset

0,3

Links

Table of n, a(n) for n=0..79.

Eric Weisstein's World of Mathematics, Harmonic Mean.

Wikipedia, Harmonic mean.

Formula

a(A011540(n)) = 0.

Example

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

Mathematica

a[n_]:=Numerator[HarmonicMean[IntegerDigits[n]]]; Array[a, 80, 0]

Prog

(Python)
from fractions import Fraction
def a(n):
    d = list(map(int, str(n)))
    return 0 if 0 in d else (len(d)/sum(Fraction(1, di) for di in d)).numerator
print([a(n) for n in range(80)]) # Michael S. Branicky, Dec 29 2025

Crossrefs

Cf. A011540, A371383, A392050 (denominator), A392051.

Sequence in context: A373102 A081286 A080867 * A095187 A218978 A309589

Adjacent sequences: A392046 A392047 A392048 * A392050 A392051 A392052

Keyword

nonn,base,easy,frac

Author

Stefano Spezia, Dec 29 2025

Status

approved