Number of quadruples (p_1, ..., p_4) of positive integers such that p_{i-1} <= p_i <= n^(i-1).

Terms

a(0) =0a(1) =1a(2) =44a(3) =541a(4) =3236a(5) =12885a(6) =39656a(7) =102249a(8) =231736a(9) =476121a(10) =905620a(11) =1618661a(12) =2748604a(13) =4471181a(14) =7012656a(15) =10658705a(16) =15764016a(17) =22762609a(18) =32178876a(19) =44639341a(20) =60885140a(21) =81785221a(22) =108350264a(23) =141747321a(24) =183315176a(25) =234580425a(26) =297274276a(27) =373350069a(28) =465001516a(29) =574681661