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%I #16 Jan 09 2021 10:01:21
%S 1,1,1,5,7,175,7601,35035,3620617,533203385,5132341123,1381418533495,
%T 19315437152429,318022715945935,176611180730425441,
%U 120653354922346558325,3031735699207849905271,86163723379372590236285,101750602671765022556964427,3623786261867543729253761465
%N a(0) = 1; for n > 0, a(n) = (-1)^(n+1)*B(2n)*Product_{prime p<=2n+1} p where B(2n) denotes the (2n)-th Bernoulli number.
%p seq(abs(bernoulli(n)*A034386(n+1)), n=0..38, 2); # _Peter Luschny_, Oct 02 2017
%t P[n_] := Times @@ Array[Prime, PrimePi[n]];
%t a[n_] := Abs[BernoulliB[2n]] P[2n+1];
%t Table[a[n], {n, 0, 19}] (* _Jean-François Alcover_, Jun 13 2019 *)
%o (PARI) a(n) = if(n==0, 1, (-1)^(n+1)*bernfrac(2*n)*prod(p=1, 2*n+1, if(isprime(p), p, 1)))
%Y Cf. A002445, A034386.
%K nonn
%O 0,4
%A _Benoit Cloitre_, Nov 11 2006