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A305665
Denominators of the fraction Sum_{n>=0} {a(n)/a(n+1)} = a(0)/a(1) + a(1)/a(2) + a(2)/a(3) + ... such that the sum has the concatenation of these denominators as decimal part. Case a(0) = 1 and a(1) = 4.
25
1, 4, 23, 937574, 9717339108198104, 997945570689257470816576227568765689032610
OFFSET
0,2
COMMENTS
It appears that there are only three sequences of this kind, with a(1) = 3 (A305664), a(1) = 4 (this sequence) and a(1) = 10 (A305666).
a(6) has 110 digits. - Giovanni Resta, Jun 08 2018
EXAMPLE
1/4 = 0.3333...
1/4 + 4/23 = 0.3407043...
1/4 + 4/23 + 23/937574= 0.34076600381136...
The sum is 0.3 407 6600381 ...
MAPLE
P:=proc(q, h) local a, b, d, n, t, x; x:=1; a:=1/h; b:=ilog10(h)+1;
d:=h; print(d); t:=1/a; for n from x to q do
if trunc(evalf(a+t/n, 100)*10^(b+ilog10(n)+1))=d*10^(ilog10(n)+1)+n then b:=b+ilog10(n)+1; d:=d*10^(ilog10(n)+1)+n; a:=a+t/n; t:=n; x:=n+1; print(n); fi; od; end: P(10^20, 4);
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Jun 08 2018
EXTENSIONS
a(4)-a(5) from Giovanni Resta, Jun 08 2018
a(0)=1 inserted. - R. J. Mathar, Jun 19 2021
STATUS
approved