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a(n) = A367338(n) - n, or -1 if A367338(n) = -1.
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%I #20 Jan 20 2024 08:50:24

%S 11,22,33,44,56,67,78,89,91,1,12,23,34,45,57,68,79,-1,91,2,13,24,35,

%T 47,58,69,-1,81,91,3,14,25,36,48,59,-1,71,81,91,4,15,26,38,49,-1,61,

%U 71,81,91,5,16,27,39,-1,51,61,71,81,91,6,17,29,-1,41,51,61,71,81,91,7,18,-1

%N a(n) = A367338(n) - n, or -1 if A367338(n) = -1.

%C Construct the commas sequence as in A121805, but take first term to be n. Then a(n) is the two digit number surrounding the first comma, or -1 if there is no second term (and hence no comma).

%C a(n) (unless it -1) is called the comma-number of n.

%C As in A121805, if the term before the comma ends in 0, that 0 is ignored and the comma number is a single-digit number.

%H N. J. A. Sloane, <a href="/A367339/b367339.txt">Table of n, a(n) for n = 1..10000</a>

%e For n = 1, A121805 begins 1, 12, 35, 94, ..., and the first comma appears as 1,1, so a(1) = 11.

%e For n = 2, A139284 begins 2, 24, 71, 89, ... and the first comma appears as 2,2, so a(2) = 22.

%e For n = 36, the commas sequence starting at 36 is simply the one-term sequence [36], no second term exists, there is no comma, and so a(36) = -1.

%Y Cf. A121805, A367338, A367340, A367341.

%K sign,base

%O 1,1

%A _N. J. A. Sloane_, Nov 15 2023