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 A287994 Position of the first time an n-digit number appears twice in a row after the decimal point of Pi. 2
 24, 413, 326, 8239, 107472, 1632152, 9719518, 106235025 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 209209 and 305305 appear in Pi before any 2-digit number appears twice in a row. LINKS Table of n, a(n) for n=1..8. EXAMPLE a(1) = 24 because the first time a 1-digit number appears twice in a row in the decimal expansion of Pi is 24 digits after the decimal point: 3.14159265358979323846264(33)... MATHEMATICA s = First@ RealDigits[Pi, 10, 10^7]; Table[p = Partition[s, k, 1]; SelectFirst[ Range[ Length[p] - k], p[[#]] == p[[# + k]] &] - 1, {k, 7}] (* Giovanni Resta, Sep 05 2017 *) PROG (Python) from sympy import S # download https://stuff.mit.edu/afs/sipb/contrib/pi/pi-billion.txt, then # with open('pi-billion.txt', 'r') as f: pi_digits = f.readline() pi_digits = str(S.Pi.n(2*10**5))[:-1] # alternative to above pi_digits = pi_digits.replace(".", "") def a(n): idx = 1 while pi_digits[idx:idx+n] != pi_digits[idx+n:idx+2*n]: idx += 1 assert idx + 2*n < len(pi_digits), "increase precision" return idx print([a(n) for n in range(1, 6)]) # Michael S. Branicky, Apr 24 2022 CROSSREFS Cf. A000796, A288291, A290977. Sequence in context: A221619 A267166 A016326 * A072975 A062193 A016268 Adjacent sequences: A287991 A287992 A287993 * A287995 A287996 A287997 KEYWORD nonn,base,more AUTHOR Bobby Jacobs, Sep 01 2017 EXTENSIONS a(8) from Michael S. Branicky, Apr 24 2022 STATUS approved

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Last modified September 25 03:27 EDT 2023. Contains 365582 sequences. (Running on oeis4.)