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A124878
Primes in A027612.
4
5, 13, 223, 4861, 197698279, 25472027467, 6975593267347, 218572480850557, 1592457339642613, 2955634782407818711841368777079578319, 2950127241932882597818337002939124083061, 232242878286351670588710938679161483012314573381293769
OFFSET
1,1
LINKS
Eric Weisstein's World of Mathematics, Harmonic Number.
FORMULA
a(n) = A027612(A124879(n)).
EXAMPLE
A027612(n) begins {1, 5, 13, 77, 87, 223, 481, 4609, 4861, ...}.
Thus a(1) = 5, a(2) = 13, a(3) = 223, a(4) = 4861.
MATHEMATICA
s=1; Do[s=s+1/(n+1); f=Numerator[(n+1)*(s-1)]; If[PrimeQ[f], Print[{n, f}]], {n, 1, 1942}]
PROG
(PARI) lista(nn) = {for (n=1, nn, if (isprime(p=numerator(sum(k=1, n, k/(n-k+1)))), print1(p, ", ")); ); } \\ Michel Marcus, Jul 14 2018
CROSSREFS
A027612(n) are the numerators of second order harmonic numbers H(n, (2)).
Corresponding numbers n such that A027612(n) is prime are listed in A124879.
Sequence in context: A209271 A352083 A355763 * A085554 A226664 A067135
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Nov 11 2006
EXTENSIONS
a(12) from, and crossrefs edited by Michel Marcus, Jul 14 2018
STATUS
approved