%I #15 Aug 02 2020 11:29:38
%S 12,18,20,25,34,36,40,44,48,56,70,72,74,80,81,88,100,104,106,108,112,
%T 121,124,134,144,156,160,162,184,192,194,196,200,202,208,218,220,228,
%U 260,268,272,274,284,288,289,300,304,314,320,324,336,346,350,352,361,368,372,386,392,394,400,416,432,441
%N Reversal numbers: union of A257719 and A257720.
%H Reinhard Zumkeller, <a href="/A263838/b263838.txt">Table of n, a(n) for n = 1..10000</a>
%H P. Pollack, C. Pomerance, <a href="https://www.researchgate.net/publication/301239790_Some_problems_of_Erdos_on_the_sum-of-divisors_function">Some problems of Erdős on the sum-of-divisors function</a>, For Richard Guy on his 99th birthday: May his sequence be unbounded, 2015, to appear.
%o (Haskell)
%o import Data.List.Ordered (union)
%o a263838 n = a263838_list !! (n-1)
%o a263838_list = union a257719_list a257720_list
%o -- _Reinhard Zumkeller_, Oct 31 2015
%Y Cf. A257719, A257720.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Oct 30 2015