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A329850
Lexicographically earliest sequence of distinct positive integers such that for any n > 0, f(n) * f(a(n)) = f(n * a(n)) where f(m) is the product of the digits of m.
1
1, 2, 3, 10, 19, 20, 30, 40, 50, 4, 60, 70, 18, 46, 80, 90, 100, 13, 5, 6, 64, 61, 28, 72, 102, 104, 62, 23, 41, 7, 110, 42, 120, 103, 106, 105, 109, 107, 130, 8, 29, 32, 140, 150, 108, 14, 160, 170, 180, 9, 190, 200, 201, 202, 83, 205, 210, 148, 204, 11, 22
OFFSET
1,2
COMMENTS
This sequence is a variant of A329804; both sequences share graphical features.
This sequence is a self-inverse permutation of the positive integers.
Keyword "look" added in view of the scatterplot of 110000 terms. - N. J. A. Sloane, Nov 23 2019
FORMULA
a(a(n)) = n.
EXAMPLE
The first terms, alongside f(n), f(a(n)) and f(n*a(n)), are:
n a(n) f(n) f(a(n)) f(n*a(n))
-- ---- ---- ------- ---------
1 1 1 1 1
2 2 2 2 4
3 3 3 3 9
4 10 4 0 0
5 19 5 9 45
6 20 6 0 0
7 30 7 0 0
8 40 8 0 0
9 50 9 0 0
10 4 0 4 0
11 60 1 0 0
12 70 2 0 0
13 18 3 8 24
14 46 4 24 96
PROG
(C) See Links section.
CROSSREFS
Sequence in context: A143045 A156909 A215121 * A175569 A275020 A122822
KEYWORD
nonn,base,look
AUTHOR
Rémy Sigrist, Nov 22 2019
STATUS
approved