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Gelfand's Question


nSloane's2^n3^n4^n5^n6^n7^n8^n9^n
1A00002723456789
2A00299349123468
3A00299482612357
4A09740818261246
5A09740932137135
6A09741067414125
7A09741112172824
8A09741226631514
9A09741351211413
10A09741415196213

Consider the leftmost (i.e., most significant) decimal digit of the numbers 2^n, 3^n, ..., 9^n. Then what are the patterns of digits occurring in the table for n=1, 2, ... (King 1994)? For example,

1. Will the digit 9 ever occur in the 2^n column? The answer is "yes," in particular at values n=53, 63, 73, 83, 93, 156, 166, 176, ... (OEIS A097415. This problem appears in Avez (1966, p. 37), where it is attributed to Gelfand.

2. Will the row "23456789" ever appear for n>1? None does for n<=10^5. If so, will it have a frequency? If so, will the frequency be rational or irrational?

3. Will a row of all the same digit occur? No such example occurs for n<=10^5.

4. Will the decimal expansion of an 8-digit prime ever occur? (The answer is "yes," in particular at values n=1, 11, 21, 44, 55, 81, 90, 118, 126, ... (OEIS A097616), corresponding to the primes 23456789, 21443183, 21442591, 19351159, ... (OEIS A097617).

Amazingly, this problem is isomorphic to Poncelet's porism (King 1994).


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References

Avez, A. Ergodic Theory of Dynamical Systems, Vol. 1. Minneapolis, MX: University of Minnesota Institute of Technology, 1966.King, J. L. "Three Problems in Search of a Measure." Amer. Math. Monthly 101, 609-628, 1994.Previato, E. "Featured Review: CRC Concise Encyclopedia of Mathematics. Second Edition." SIAM Rev. 46, 349-354, 2004.Sloane, N. J. A. Sequences A000027/M0472, A002993/M3348, A002994/M4468, A097408, A097409, A097410, A097411, A097412, A097413, A097414, A097415, A097616, and A097617 in "The On-Line Encyclopedia of Integer Sequences."

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Gelfand's Question

Cite this as:

Weisstein, Eric W. "Gelfand's Question." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/GelfandsQuestion.html

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