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A110936 a(n) = denominator(Bernoulli(prime(n) - 1))/prime(n).

%I A110936 #18 Mar 31 2019 04:53:22
%S A110936 1,2,6,6,6,210,30,42,6,30,462,51870,330,42,6,30,6,930930,966,66,
%T A110936 1919190,42,6,690,46410,330,42,6,1919190,14790,34314,66,30,1974,30,
%U A110936 14322,11430510,798,6,30,6,39921071190,66,4501770,870,1229718,43725066,42,6
%N A110936 a(n) = denominator(Bernoulli(prime(n) - 1))/prime(n).
%F A110936 6 divides a(n) for n >= 3. a(n) is squarefree. - _Peter Luschny_, Mar 30 2019
%e A110936 From _Peter Luschny_, Mar 30 2019: (Start)
%e A110936 n = 12 -> prime(12) - 1 = 37 - 1 = 36,
%e A110936 D = divisors(36) \ {36} = {1, 2, 3, 4, 6, 9, 12, 18},
%e A110936 P = {p: (p-1) in D, p prime} = {2, 3, 5, 7, 13, 19},
%e A110936 Product(P) = 51870 = a(n).
%e A110936 .
%e A110936 n = 18 -> prime(18) - 1 = 61 - 1 = 60,
%e A110936 D = divisors(60) \ {60} = {1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30},
%e A110936 P = {p: (p-1) in D, p prime} = = {2, 3, 5, 7, 11, 13, 31},
%e A110936 Product(P) = 930930 = a(n).
%e A110936 (End)
%p A110936 a := proc(n) if not isprime(n+1) then return NULL fi;
%p A110936 numtheory[divisors](n) minus {n};
%p A110936 map(i->i+1, %); mul(i, i=select(isprime, %)) end:
%p A110936 seq(a(n), n=1..226); # _Peter Luschny_, Mar 30 2019
%t A110936 a[n_] := (p = Prime[n]; Denominator[ BernoulliB[p - 1]]/p); Table[a[n], {n, 1, 49}] (* _Jean-François Alcover_, Dec 13 2012 *)
%Y A110936 Cf. A000040, A002445.
%K A110936 easy,nonn,frac
%O A110936 1,2
%A A110936 _Vladeta Jovovic_, Jan 21 2006