OFFSET
1,3
COMMENTS
Smallest element in row n of irregular triangle in A323460.
Theorem: Let the decimal expansion of n be d_1 d_2 ... d_k. (i) If there is a substring d_r ... d_s which starts with d_r = 1 and ends with an even digit d_s = e, take that string which starts with the leftmost 1 and ends with the rightmost even digit, and halve it. (ii) Otherwise, if there is an even digit e, take the substring from d_1 to the rightmost such e and halve it. (iii) Otherwise, all d_i are odd, and a(n) = n.
LINKS
Eric Angelini, Lars Blomberg, Charlie Neder, Remy Sigrist, and N. J. A. Sloane, "Choix de Bruxelles": A New Operation on Positive Integers, arXiv:1902.01444, Feb 2019; Fib. Quart. 57:3 (2019), 195-200.
EXAMPLE
From 23 we can reach any of 13, 43, 26, 46, and the smallest of these is a(23) = 13.
CROSSREFS
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Jan 23 2019
STATUS
approved