A375526 - OEIS

%I #14 Aug 31 2024 08:32:11

%S 2,6,30,210,420,420,1260,126,3150,97650,830025,6640200,6640200,

%T 312089400,312089400,9050592600,72404740800,4851117633600,

%U 354131587252800,4603710634286400,4603710634286400,197959557274315200,15227658251870400,1477082850431428800,78285391072865726400

%N a(n) = denominator of Sum_{i=1..n} 1/A031216(i).

%H Alois P. Heinz, <a href="/A375526/b375526.txt">Table of n, a(n) for n = 1..882</a>

%e The first few fractions are 1/2, 5/6, 31/30, 247/210, 529/420, 559/420, 1747/1260, 181/126, 4651/3150, 147331/97650, 1276726/830025, 10379813/6640200, 10527373/6640200, ...

%p b:= n-> (l-> add(l[i]*11^(i-1), i=1..nops(l)))(convert(ithprime(n),base,10)):

%p g:= proc(n) option remember; `if`(n<1, 0, g(n-1)+1/b(n)) end:

%p a:= n-> denom(g(n)):

%p seq(a(n), n=1..25);  # _Alois P. Heinz_, Aug 30 2024

%o (PARI) a(n) = denominator(sum(i=1, n, 1/fromdigits(digits(prime(i)), 11))); \\ _Michel Marcus_, Aug 31 2024

%Y Cf. A031216, A375525.

%K nonn,frac

%O 1,1

%A _N. J. A. Sloane_, Aug 30 2024