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A367616
a(n) is the unique k such that n is a comma-child of k, or -1 if k does not exist.
3
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 10, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 20, 11, 2, -1, -1, -1, -1, -1, -1, -1, -1, 30, 21, 12, 3, -1, -1, -1, -1, -1, -1, -1, 40, 31, 22, 13, 4, -1, -1, -1, -1, -1, -1, 50, 41, 32, 23, 14, 14, 5, -1, -1, -1, -1, 60, 51, 42, 33, 33, 24, 15, 6, -1, -1, -1, 70, 61, 52, 52, 43, 34, 25, 16, 7
OFFSET
1,11
COMMENTS
Similar to A367614, but here we give the k such that n is a comma-child of k, whereas in A367614 n has to be a comma-successor of k. See A367338 for definitions.
The first difference between A367614 and the present sequence arises because 14 has one comma-successor, 59, but has two comma-children, 59 and 60. So A367614(59) = 14, A367614(60) = -1, while in the present sequence we have a(59) = a(60) = 14.
There are similar differences at n = 69 and 70, because both are comma-children of 33, and at many other places.
LINKS
PROG
(Python)
def a(n):
y = int(str(n)[0])
x = (n-y)%10
k = n - y - 10*x
return k if k > 0 else -1
print([a(n) for n in range(1, 86)]) # Michael S. Branicky, Dec 18 2023
CROSSREFS
KEYWORD
sign,base
AUTHOR
N. J. A. Sloane, Dec 18 2023
STATUS
approved