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A348017
Numbers k such that the numerator of the fractional part of the k-th harmonic is a prime number.
1
3, 5, 7, 9, 10, 12, 19, 21, 24, 29, 34, 39, 45, 46, 54, 65, 84, 86, 116, 128, 161, 177, 248, 254, 274, 297, 349, 352, 412, 422, 475, 493, 636, 747, 793, 811, 855, 864, 1012, 1060, 1074, 1097, 1127, 1139, 1152, 1299, 1371, 1423, 1785, 1847, 1872, 1873, 2072, 2326
OFFSET
1,1
COMMENTS
The corresponding primes are 5, 17, 83, 2089, 2341, 2861, 42503239, 3338549, 276977179, 2239777822987, ...
LINKS
EXAMPLE
3 is a term since 1 + 1/2 + 1/3 = 11/6, the fractional part of 11/6 is 5/6 and its numerator, 5, is prime.
5 is a term since 1 + 1/2 + 1/3 + 1/4 + 1/5 = 137/60, the fractional part of 137/60 is 17/60 and its numerator, 17, is prime.
MATHEMATICA
s = 0; seq = {}; Do[s += 1/n; If[PrimeQ @ Numerator @ FractionalPart[s], AppendTo[seq, n]], {n, 1, 2500}]; seq
PROG
(Python)
from sympy import harmonic, isprime
A348017_list = [k for k in range(10**3) if isprime((lambda x: x.p % x.q)(harmonic(k)))] # Chai Wah Wu, Sep 26 2021
CROSSREFS
Sequence in context: A376692 A358529 A080207 * A187347 A187413 A091177
KEYWORD
nonn
AUTHOR
Amiram Eldar, Sep 24 2021
STATUS
approved