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A326776
a(n) is the smallest divisor of the n-th nonprime number (A018252(n)) not already in the sequence.
1
1, 2, 3, 4, 9, 5, 6, 7, 15, 8, 18, 10, 21, 11, 12, 25, 13, 27, 14, 30, 16, 33, 17, 35, 36, 19, 39, 20, 42, 22, 45, 23, 24, 49, 50, 51, 26, 54, 55, 28, 57, 29, 60, 31, 63, 32, 65, 66, 34, 69, 70, 72, 37, 75, 38, 77, 78, 40, 81, 41, 84, 85, 43, 87, 44, 90, 91
OFFSET
1,2
COMMENTS
This sequence is a permutation of the natural numbers.
Empirically:
- the subsequence with the terms satisfying a(n) <= n correspond to A093641,
- if a(n) > n, then a(n) = A018252(n),
- these two situations appear as two lines in the scatterplot of the sequence.
EXAMPLE
The first terms, alongside the divisors of A018252(n), are:
n a(n) div(A018252(n))
-- ---- ---------------
1 1 (1)
2 2 (1, 2, 4)
3 3 (1, 2, 3, 6)
4 4 (1, 2, 4, 8)
5 9 (1, 3, 9)
6 5 (1, 2, 5, 10)
7 6 (1, 2, 3, 4, 6, 12)
8 7 (1, 2, 7, 14)
9 15 (1, 3, 5, 15)
10 8 (1, 2, 4, 8, 16)
PROG
(PARI) See Links section.
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Jul 28 2019
STATUS
approved