A320023 Denominators a(n) of the fractions Sum_{n>=1} {(-1)^(n+1)*n/a(n)} = 1/a(1) - 2/a(2) + 3/a(3) - ... such that the sum has the concatenation of these denominators as decimal part. Case a(1) = 3.

3, 254, 91945, 73232344999, 9786553139540254602022, 472979128067981514720595568770925883088312456

Offset

1,1

Comments

a(7) has 89 digits. - Giovanni Resta, Oct 11 2018

Links

Table of n, a(n) for n=1..6.

Example

1/3 = 0.333...
1/3 - 2/254 = 0.32545931...
1/3 - 2/254 + 3/91945 = 0.3254919457869...
The sum is 0.3 254 91945 ...

Maple

P:=proc(q, h) local a, b, d, n, t; a:=1/h; b:=ilog10(h)+1; d:=h;
print(d); t:=-2; for n from 1 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:=(-1)^abs(t)*(abs(t)+1); print(n); fi; od; end: P(10^20, 3);

Crossrefs

Cf. A304288, A304289, A305661, A305662, A305663.

Sequence in context: A213409 A227028 A279653 * A364876 A045824 A027860

Adjacent sequences: A320020 A320021 A320022 * A320024 A320025 A320026

Keyword

nonn,base

Author

Paolo P. Lava, Oct 03 2018

Extensions

a(4)-a(6) from Giovanni Resta, Oct 11 2018

Status

approved