A121595 Compressed version of A119788 (all entries equal to 1 are excluded).

5, 7, 5, 11, 13, 17, 7, 29, 7, 37, 19, 47, 119, 41, 23, 5, 29, 31, 11, 37, 37, 41, 43, 71, 13, 7, 13, 13, 47, 13, 49, 7, 7, 7, 53, 5, 79, 59, 97, 61, 71, 103, 67, 17, 71, 61, 73, 139, 17, 17, 79, 19, 19, 19, 83, 19, 151, 89, 29, 29, 263, 97

Offset: 1

Author

Alexander Adamchuk, Aug 09 2006

Keywords

• nonn

Comments

Also the ratio of the numerators of n*H'(n) = A119787(n) and H'(n) = A058313(n) when they are different. (H'(n) is the alternating harmonic number H'(n) = Sum_{k=1..n} (-1)^(k+1)*1/k.)

The ratio of numerators A119787(n)/A058313(n) for n = 1..400 is given in A119788(n).

It appears that most a(n) are prime divisors of the corresponding indices A121594(n).

The first and only composite a(n) up to A119788(6000) is a(31) = 49 corresponding to A119788(1470).

It appears that all a(n) belong to A092579(n), which is a sieve using the Fibonacci sequence over the integers >= 2. [Edited by Petros Hadjicostas, May 11 2020]

Crossrefs

Cf. A058313, A092579, A119787, A119788, A121594.

Programs

Mathematica

Do[H=Sum[(-1)^(i+1)*1/i, {i, 1, n}]; a=Numerator[n*H]; b=Numerator[H]; If[ !Equal[a,b],Print[{n,a/b}]], {n,1,6000}]

Formula

a(n) = A119788(A121594(n)), while the corresponding indices are given in A121594(n).