A112813 Numbers k such that lcm(1,2,3,...,k)/3 equals the denominator of the k-th harmonic number H(k).

6, 7, 8, 18, 19, 25, 26, 54, 55, 56, 57, 58, 59, 60, 61, 62, 72, 73, 74, 75, 76, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231

Offset: 1

Author

Robert G. Wilson v, Sep 17 2005

Keywords

• nonn

Comments

When 3 occurs in A110566.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002805, A003418, A110566.

Cf. A098464, A112814, A112815, A112816, A112817, A112818, A112819, A112820, A112821, A112822.

Programs

Mathematica

f[n_] := LCM @@ Range[n]/Denominator[ HarmonicNumber[n]]; Select[ Range[231], f[ # ] == 3 &]

PARI

isok(n) = lcm(vector(n, i, i)) == 3*denominator(sum(i=1, n, 1/i)); \\ Michel Marcus, Mar 07 2018