OFFSET
1,2
COMMENTS
Partial sum of a(n) digits of decimal expansion of pi equals an integer N * a(n).
If Pi is normal then average digit in limit = 4.5.
Related to drunkard's walk? How many times does the drunkard's walk cross the x-axis?
No more terms below 5,000,000. - Harvey P. Dale, Apr 07 2010
EXAMPLE
a(2)=3 because the first 3 decimal places of Pi, the digits are 1+4+1, has an integer average of 6/3 = 2.
Pi = 3.14159 26...
Digit sums 1, 5=1+4, 6=1+4+1, 11, 20, 22, 28...
Number of digits =1, 2, 3, 4, 5, 6, 7.
Average 1, 2.5, 2, 2.75, 4, 3.7,4...
Average is a whole number: 1, 2, 4, 4 ...
When number of digits equals a(n) = 1 3 5 7 9 13 20.
1 = 1*1, compressed ... 11
6 = 2*3, compressed ... 23
20 = 4*5, compressed ... 45
28 = 4*7, compressed ... 47
36 = 4*9, compressed ... 49
65 = 5*13, compressed ... 513
100 = 5*20, compressed ... 520.
MATHEMATICA
Block[{i = 30000, z = RealDigits[Pi - 3, 10, 30000][[1]], lst = {}}, While[z != {}, If[Divisible[Total[z], i], PrependTo[lst, i]]; i--; z = Most@z; ]; lst] (* J. Mulder (jasper.mulder(AT)planet.nl), Jan 25 2010 *)
lst=Accumulate[ Rest[ RealDigits[ N[ \[ Pi ], 5000001 ] ][ [ 1 ] ] ] ]; Transpose[ Select[ Partition[ Flatten[ Table[ {n, (Take[ lst, {n} ])/n}, {n, 5000000} ], 2 ], 2 ], IntegerQ[ #[ [ 2 ] ] ]& ] ][ [ 1 ] ] (* Harvey P. Dale, Apr 07 2010 *)
CROSSREFS
KEYWORD
base,more,nonn
AUTHOR
Donald S. McDonald, Mar 22 2007
EXTENSIONS
Corrected and extended by J. Mulder (jasper.mulder(AT)planet.nl), Jan 25 2010
Edited by Max Alekseyev, Oct 14 2012
STATUS
approved