A367339 a(n) = A367338(n) - n, or -1 if A367338(n) = -1.

11, 22, 33, 44, 56, 67, 78, 89, 91, 1, 12, 23, 34, 45, 57, 68, 79, -1, 91, 2, 13, 24, 35, 47, 58, 69, -1, 81, 91, 3, 14, 25, 36, 48, 59, -1, 71, 81, 91, 4, 15, 26, 38, 49, -1, 61, 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

Offset: 1

Author

N. J. A. Sloane, Nov 15 2023

Keywords

• sign
• base

Comments

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).

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

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.

Examples

			For n = 1, A121805 begins 1, 12, 35, 94, ..., and the first comma appears as 1,1, so a(1) = 11.
For n = 2, A139284 begins 2, 24, 71, 89, ... and the first comma appears as 2,2, so a(2) = 22.
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.
		

Links

• N. J. A. Sloane, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A121805, A367338, A367340, A367341.