cp's OEIS Frontend

A064810 Self-locating strings within Pi: numbers n such that the string n is at position n in the decimal digits of Pi, where 1 is the 0th digit.

%I A064810 #63 Aug 12 2024 13:17:20
%S A064810 6,27,13598,43611,24643510,71683711,78714901,268561754,4261759184,
%T A064810 82638677082,548535559133,8773143366618
%N A064810 Self-locating strings within Pi: numbers n such that the string n is at position n in the decimal digits of Pi, where 1 is the 0th digit.
%C A064810 Near-misses '04658726522' and '0769960191236' occur at positions 4658726522 and 769960191236, respectively. - _Kang Seonghoon_, Nov 02 2020
%C A064810 a(13) > 5 * 10^13. - _Kang Seonghoon_, Nov 02 2020
%H A064810 Dave Andersen, <a href="http://www.angio.net/pi/piquery">The Pi-Search Page</a>.
%H A064810 Tom Crawford and Brady Haran, <a href="https://www.youtube.com/watch?v=W20aT14t8Pw">Strings and Loops within Pi</a>, Numberphile video (2020).
%H A064810 Brady Haran and Katie Steckles, <a href="http://www.youtube.com/watch?v=euAHY9hqRN4">27 the Favourite Number</a>, Numberphile video (2012).
%H A064810 Timothy Mullican, <a href="https://web.archive.org/web/20220610074058/http://storage.googleapis.com/pi50t/index.html">50 trillion digits of pi</a> (2020). Last backup of the googleAPIs.com page on web.archive.org, as of June 2022.
%H A064810 L. Brandon Stone, <a href="https://web.archive.org/web/20041016044314/http://www.lbstone.com/27/science/pi.html">27 and the Number Pi</a>, personal web site. Last backup on web.archive.org as of Oct. 2004.
%e A064810 6 is the first term because Pi is 3.1415926... and the digit 6 is in position 6 after the decimal point when the first 1 after the decimal point is considered to be at position 0.
%t A064810 Do[If[RealDigits[Pi,10,a=i+IntegerLength@i-1,-2][[1,i;;a]]==IntegerDigits@i,Print@i],{i,50000}] (* _Giorgos Kalogeropoulos_, Feb 21 2020 *)
%o A064810 (Python)
%o A064810 # download https://stuff.mit.edu/afs/sipb/contrib/pi/pi-billion.txt, then
%o A064810 with open('pi-billion.txt', 'r') as f: digits_of_pi = f.readline()[2:]
%o A064810 # from sympy import S, isprime
%o A064810 # digits_of_pi = str(S.Pi.n(3*10**5))[2:] # alternate to loading data
%o A064810 def afind():
%o A064810     global digits_of_pi
%o A064810     for k in range(len(digits_of_pi)):
%o A064810         s = str(k)
%o A064810         if digits_of_pi[k:k+len(s)] == s: print(k, end=", ")
%o A064810 afind() # _Michael S. Branicky_, Jun 27 2021
%Y A064810 Cf. A000796, A057679, A057680.
%K A064810 base,nonn,more
%O A064810 1,1
%A A064810 Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Oct 22 2001
%E A064810 a(6)-a(10) from _Alan Eliasen_, May 11 2013
%E A064810 a(11) from _Alan Eliasen_, May 28 2013
%E A064810 a(12) added and name clarified by _Kang Seonghoon_, Nov 02 2020
%E A064810 Error in a(11) reported by Sergey Prokudin, edited by _Robert Price_, Mar 14 2022