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a(0) = 1, a(n) = (denominator of the Bernoulli number B_{2n})/3, for n>=1.
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%I #50 Dec 16 2016 14:17:53

%S 1,2,10,14,10,22,910,2,170,266,110,46,910,2,290,4774,170,2,639730,2,

%T 4510,602,230,94,15470,22,530,266,290,118,18928910,2,170,21574,10,

%U 1562,46700290,2,10,1106,76670,166,1134770,2,20470,90706,470,2,1500590,2,11110,1442,530,214,69730570,506,557090,14,590,2,776085310

%N a(0) = 1, a(n) = (denominator of the Bernoulli number B_{2n})/3, for n>=1.

%C All terms except a(0) are odd multiples of 2, by the von Staudt-Clausen theorem. See A002445 and A027642 for comments, references, and links.

%H Robert Israel, <a href="/A277087/b277087.txt">Table of n, a(n) for n = 0..10000</a>

%F a(0) = 1, a(n) = (1/3)*A002445(n) = (1/3)*A027642(2*n) = (2/3)*A001897(n) for n>0.

%p 1, seq(denom(bernoulli(2*n))/3,n=1..100); # _Robert Israel_, Dec 16 2016

%t Join[{1}, Denominator[BernoulliB[Range[2, 120, 2]]]/3]

%o (PARI) a(n)=ceil(denominator(bernfrac(2*n))/3) \\ _Charles R Greathouse IV_, Dec 16 2016

%Y Cf. A001897, A002445, A027642.

%K nonn,frac

%O 0,2

%A _Jonathan Sondow_, Dec 12 2016