[seqfan] A sum visible in the 2d integer
Eric.Angelini at kntv.be
Wed Feb 3 13:30:48 CET 2016
Is S the lexico-first permutation of the non-negative integers?
S = 0,1,12,13,14,15,16,17,18,19,10,2,24,26,28,109,100,3,25,27,29,...
The rules for expanding S are:
# Say a(n) and a(n+1) are two consecutive integers of S;
# Add the last digit of a(n) to the first digit of a(n+1)
# The result must be a substring of a(n+1)
# a(n+1) cannot be an integer already in S.
We see here that
0+1 = 1 which is visible in 1
1+1 = 2 which is visible in 12
2+1 = 3 which is visible in 13
3+1 = 4 which is visible in 14
9+1 = 10 which is visible in 10
0+2 = 2 which is visible in 2
2+2 = 4 which is visible in 24
The term after 28 cannot be 19 (though 8+1 = 9 which is visible in 19)
because 19 was already used before. So 109 has been selected.
This is tricky to compute by hand. Hope no typos were left.
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