A351904 a(n) is the smallest number k such that the symmetric representation of sigma(k) has at least one subpart n.
1, 3, 2, 7, 9, 11, 4, 15, 10, 19, 6, 14, 24, 27, 8, 31
Offset: 1
Examples
For n = 11 we have that 6 is the smallest number k with at least one subpart 11 in the symmetric representation of sigma(k), so a(11) = 6.
The symmetric representation of sigma(6) in the first quadrant looks like this:
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_ _ _ _
|_ _ _ |_ 1
| |_|_ 11
|_ _ |
| |
| |
|_|
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There are one subpart 11 and one subpart 1.
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Some pairs of the form a(x) = y; a(y) = x:
a(2) = 3; a(3) = 2.
a(4) = 7; a(7) = 4.
a(6) = 11; a(11) = 6.
a(8) = 15; a(15) = 8.
a(16) = 31; a(31) = 16.
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