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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
25, 121, 125, 126, 127, 128, 153, 216, 289, 343, 347, 625, 688, 736, 1022, 1024, 1206, 1255, 1260, 1285, 1296, 1395, 1435, 1503, 1530, 1792, 1827, 2048, 2187, 2349, 2500, 2501, 2502, 2503, 2504, 2505, 2506, 2507, 2508, 2509, 2592, 2737, 2916, 3125, 3159 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
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
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
LINKS
M. F. Hasler, Table of n, a(n) for n = 1..844 (data from E. Friedman's page as collected by K. Mitchell, completed by the two missing terms found by G. Resta).
M. Brand, Friedman numbers have density 1, Discrete Applied Mathematics, Volume 161, Issues 16-17, November 2013, Pages 2389-2395.
Ed Copeland and Brady Haran, Friedman numbers, Numberphile video, 2014
Erich Friedman, Friedman Numbers
Giovanni Resta, Friedman numbers Friedman numbers and expressions up to 10^6
FORMULA
a(n) ~ n, see Brand. - Charles R Greathouse IV, Jun 04 2013
EXAMPLE
E.g., 153=51*3, 736=3^6+7. Not 26 = 2 6 (concatenated), that's trivial.
CROSSREFS
Sequence in context: A078815 A270368 A206472 * A083509 A343075 A339130
KEYWORD
base,nonn
AUTHOR
EXTENSIONS
Edited by Michel Marcus and M. F. Hasler, Jan 04 2015
STATUS
approved

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Last modified March 29 08:48 EDT 2024. Contains 371268 sequences. (Running on oeis4.)