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A244861 Consider the concatenation in ascending order of the first x natural numbers and then concatenate its reverse. Sequence gives the decimal expansion of the sum of the reciprocals of such numbers. 1
0, 0, 9, 1, 7, 3, 6, 2, 8, 2, 4, 7, 4, 1, 9, 3, 3, 7, 2, 5, 0, 0, 2, 9, 5, 9, 8, 4, 2, 9, 8, 2, 9, 3, 9, 5, 0, 9, 3, 2, 0, 7, 5, 2, 7, 3, 0, 0, 9, 2, 8, 1, 4, 2, 5, 7, 2, 9, 3, 5, 1, 1, 3, 6, 0, 3, 2, 9, 5, 6, 0, 8, 7, 6, 6, 6, 9, 6, 7, 8, 2, 7, 0, 7, 6, 2, 4 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Decimal expansion of 1/11 + 1/1221 + 1/123321 + ... + 1/123456789987654321 +

1/1234567891001987654321 + 1/12345678910111101987654321 + 1/123456789101112211101987654321 + ...

0.0917362824741933725002959842982939... = [0, 10, 1, 9, 12, 4, 1, 3, 6].

Rational approximation up to the 11th decimal digit: 14649/159686.

LINKS

Table of n, a(n) for n=1..87.

MAPLE

with(numtheory): T:=proc(w) local x, y, z; x:=w; y:=0;

for z from 1 to ilog10(x)+1 do y:=y*10+(x mod 10); x:=trunc(x/10); od; y: end:

P:=proc(q) local a, b, n; a:=0; b:=0; for n from 1 to q do

a:=trunc(a/10^((ilog10(a)+1)/2))*10^(ilog10(n)+1)+n; a:=a*10^(ilog10(a)+1)+T(a);

b:=b+1/a; od; evalf(b, 500); end: P(300);

CROSSREFS

Sequence in context: A280703 A141749 A117017 * A058969 A021113 A019948

Adjacent sequences:  A244858 A244859 A244860 * A244862 A244863 A244864

KEYWORD

nonn,easy,cons,base

AUTHOR

Paolo P. Lava, Nov 12 2014

STATUS

approved

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Last modified October 18 02:23 EDT 2019. Contains 328135 sequences. (Running on oeis4.)