A228151 - OEIS

%I #21 Sep 08 2022 08:46:05

%S 1,1,1,2,3,6,5,30,105,70,35,70,231,2310,143,30030,15015,10010,85085,

%T 170170,373065,25194,323323,1939938,22309287,14872858,168245,74364290,

%U 15935205,223092870,1078282205,588153930,20056049013,5142576670,393255863,9550499530

%N Denominators of r(n) = r(n-1) + r(n-2) + B_(n-2), where B_n is the n-th Bernoulli number A027641(n)/A027642(n).

%C r(n): 0, 0, 1, 1/2, 5/3, 13/6, 19/5, 179/30, 1028/105, 1103/70, 893/35,... = A227500(n)/a(n). a(0)=a(1)=1 is a choice.

%o (PARI) r(n) = if (n<=1, 0, r(n-1) + r(n-2) + bernfrac(n-2));

%o a(n) = if (n<=1, 1, denominator(r(n))); \\ _Michel Marcus_, Aug 24 2013

%o (Magma) t:=40; r:=[n le 2 select 0 else Self(n-1)+Self(n-2)+BernoulliNumber(n-3): n in [1..t]]; [n le 2 select 1 else Denominator(r[n]): n in [1..t]]; // _Bruno Berselli_, Sep 05 2013

%Y Cf. A227500: numerators of r(n), where a(n) is named c(n).

%Y Cf. A027641, A027642.

%K nonn,frac

%O 0,4

%A _Paul Curtz_, Aug 13 2013

%E More terms from _Michel Marcus_, Aug 24 2013