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A212197
Numbers k that divide the 3k-th Clausen number.
0
1, 2, 6, 14, 42, 114, 602, 798, 1806, 5334, 34314, 101346, 229362, 4357878, 9786714, 12198858, 168241542, 185947566, 231778302, 524550894
OFFSET
1,2
COMMENTS
The classical Clausen numbers are given in A141056. See A160014 for generalizations. Related sequences are A014117 and A106741.
MATHEMATICA
(* This program is not convenient for more than 15 terms *) c[n_] := Sum[Boole[PrimeQ[d+1]]/(d+1), {d, Divisors[n]}] // Denominator; Reap[For[n = 1, n < 10^7, n++, If[Divisible[c[3*n], n], Print[n]; Sow[n]]]][[2, 1]] (* Jean-François Alcover, May 21 2013 *)
PROG
(PARI)
A212197_list(searchlimit) =
{
for (n=1, searchlimit,
p = 1;
fordiv(3*n, d,
r = d + 1;
if (isprime(r), p = p*r; )
);
if (Mod(p, n) == 0, print1(n, ", "));
);
}
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Peter Luschny, May 05 2012
STATUS
approved