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A121595
Compressed version of A119788 (all entries equal to 1 are excluded).
2
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
1,1
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]
FORMULA
a(n) = A119788(A121594(n)), while the corresponding indices are given in A121594(n).
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}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Aug 09 2006
STATUS
approved