A007523
Primes in A092845 (decimal expansion of Pi written backwards).
Original entry on oeis.org
3, 13, 51413, 951413, 2951413, 53562951413, 979853562951413
Offset: 1
51413 is in the list because it is prime and its decimal reversal, 31415, is the first 5 digits of Pi.
- M. Gardner, Whys and Wherefores, Univ. Chicago Press, 1989, p. 84.
- N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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Module[{nn=1000,rd},d=RealDigits[Pi,10,nn][[1]];Select[Table[FromDigits[Reverse[Take[d,n]]],{n,nn}],PrimeQ]] (* Harvey P. Dale, Jul 11 2023 *)
A371720
a(n) = m^^m mod 10^len(m), where m = A038399(n) and ^^ indicates tetration or hyper-4.
Original entry on oeis.org
1, 11, 811, 3811, 63811, 763811, 3763811, 5103763811, 515103763811, 19515103763811, 6819515103763811, 8146819515103763811, 3808146819515103763811, 7213808146819515103763811, 9807213808146819515103763811, 4939807213808146819515103763811
Offset: 1
a(8) is given by the rightmost 10 digits of 2113853211^^2113853211 and thus a(8) = 5103763811.
a(9) == a(8) (mod 10^10), i.e., the digits of a(9) end with the digits of a(8) (and then a(9) has 2 more preceding).
- Marco Ripà, La strana coda della serie n^n^...^n, Trento, UNI Service, Nov 2011, page 60. ISBN 978-88-6178-789-6
- Marco Ripà, The congruence speed formula, Notes on Number Theory and Discrete Mathematics, 2021, 27(4), 43-61.
- Marco Ripà and Luca Onnis, Number of stable digits of any integer tetration, Notes on Number Theory and Discrete Mathematics, 2022, 28(3), 441-457.
- Wikipedia, Tetration.
A254898
Read the first n decimal digits of Pi-3 backwards.
Original entry on oeis.org
1, 41, 141, 5141, 95141, 295141, 6295141, 56295141, 356295141, 5356295141, 85356295141, 985356295141, 7985356295141, 97985356295141, 397985356295141, 2397985356295141, 32397985356295141, 832397985356295141, 4832397985356295141, 64832397985356295141, 264832397985356295141
Offset: 1
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Module[{nn=30,pd},pd=Rest[RealDigits[Pi,10,nn][[1]]];Table[FromDigits[ Reverse[ Take[pd,n]]],{n,nn-1}]] (* Harvey P. Dale, Feb 07 2019 *)
A282183
Numbers k such that the reverse of the first k digits in the decimal expansion of Pi forms a prime.
Original entry on oeis.org
1, 2, 5, 6, 7, 11, 15, 712, 7599, 13280, 13281, 21598, 23233
Offset: 1
1 is a term as the first digit of pi, 3, reversed is prime. 2 is a term as the first two digits of pi, 31, reversed is prime. 3 is not a term as the first three digits of pi, 314, reversed, is not prime. - _David A. Corneth_, Feb 13 2017
- Shyam Sunder Gupta, Mystery of pi, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 19, 473-497.
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Do[If[PrimeQ[FromDigits[Reverse[IntegerDigits[Floor[Pi*10^(n - 1)]]]]],Print[n]],{n, 13335}]
Module[{pid=RealDigits[Pi,10,20000][[1]]},Select[Range[16000],PrimeQ[ FromDigits[ Reverse[Take[pid,#]]]]&]] (* Harvey P. Dale, Sep 06 2019 *)
Showing 1-4 of 4 results.
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