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A036057 Friedman numbers: can be written in a nontrivial way using their digits and the operations + - * / ^ and concatenation of digits (but not of results). 13

%I

%S 25,121,125,126,127,128,153,216,289,343,347,625,688,736,1022,1024,

%T 1206,1255,1260,1285,1296,1395,1435,1503,1530,1792,1827,2048,2187,

%U 2349,2500,2501,2502,2503,2504,2505,2506,2507,2508,2509,2592,2737,2916,3125,3159

%N Friedman numbers: can be written in a nontrivial way using their digits and the operations + - * / ^ and concatenation of digits (but not of results).

%C Mitchell's and Wilson's lists both lack two terms, 16387 = (1-6/8)^(-7)+3 and 41665 = 641*65. - _Giovanni Resta_, Dec 14 2013

%C Primes in this sequence are listed in A112419. See also the subsequence A080035 of "orderly" terms, and its subset A156954. - _M. F. Hasler_, Jan 04 2015

%H M. F. Hasler, <a href="/A036057/b036057.txt">Table of n, a(n) for n = 1..844</a> (data from E. Friedman's page as collected by K. Mitchell, completed by the two missing terms found by G. Resta).

%H M. Brand, <a href="http://dx.doi.org/10.1016/j.dam.2013.05.027">Friedman numbers have density 1</a>, Discrete Applied Mathematics, Volume 161, Issues 16-17, November 2013, Pages 2389-2395.

%H Ed Copeland and Brady Haran, <a href="https://www.youtube.com/watch?v=I7v2wAXFQpc">Friedman numbers</a>, Numberphile video, 2014

%H Erich Friedman, <a href="http://www.stetson.edu/~efriedma/mathmagic/0800.html">Friedman Numbers</a>

%H Giovanni Resta, <a href="http://www.numbersaplenty.com/set/Friedman_number/">Friedman numbers</a> Friedman numbers and expressions up to 10^6

%H Robert G. Wilson v, <a href="/A036057/a036057.txt">Table of n, a(n) with factorizations for n=1..844</a>

%H <a href="/index/Fo#4x4">Index entries for Four 4's problem</a>

%F a(n) ~ n, see Brand. - _Charles R Greathouse IV_, Jun 04 2013

%e E.g., 153=51*3, 736=3^6+7. Not 26 = 2 6 (concatenated), that's trivial.

%Y Cf. A080035, A156954, A046469.

%K base,nonn

%O 1,1

%A _Erich Friedman_

%E Edited by _Michel Marcus_ and _M. F. Hasler_, Jan 04 2015

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Last modified March 29 20:20 EDT 2020. Contains 333117 sequences. (Running on oeis4.)