A201545 - OEIS

%I #13 Feb 22 2017 20:38:06

%S 47,281,381,399,515,648,918,928,1303,1538,3746

%N Numbers n such that the n-th digit (after the decimal point) in the decimal expansion of Pi are the occurrence of the least significant digit represented by the more significant digits

%C The 47th digit after the decimal point in the expansion of Pi (A000796, but without the leading 3) is the 4th occurrence of the digit 7; the 281st is the 28th occurrence of the digit 1; etc.

%C Only individual least significant digits are included. Does not include, for example, 467, which is the beginning position of the 4th occurrence of 67.

%H Dave Andersen, <a href="http://www.angio.net/pi/piquery">Pi-Search Page</a>

%e The 399th digit after the decimal point in Pi is the 39th occurrence of the digit 9.

%e 225 is not in the sequence, as the 225th digit is 5, but this is the 23rd occurrence of the digit 5 in the expansion of pi, not the 22nd.

%p Digits := 4000 ;

%p pdg := proc(n)

%p         floor(Pi*10^n) mod 10 ;

%p end proc:

%p dfreq := Vector(10,0) ;

%p for n from 1 do

%p         d := pdg(n) ;

%p         dfreq[d+1] := dfreq[d+1]+1 ;

%p         ld := n mod 10 ;

%p         hid := floor(n/10) ;

%p         if dfreq[d+1] = hid and ld = d then

%p                 print(n);

%p         end if;

%p end do: # _R. J. Mathar_, Dec 16 2011

%Y Cf. A000796, A057680.

%K nonn,base

%O 1,1

%A _Matthew Goers_, Dec 02 2011