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EXAMPLE
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a(4) = 17. The 17 transformation pairs of length 4 are:
{1, 2, 3, 4} = S({1, 2, 6, 24}).
{1, 2, 3, 5} = S({1, 2, 6, 15}).
{1, 2, 3, 6} = S({1, 2, 6, 12}).
{1, 2, 3, 9} = S({1, 2, 6, 9}).
{1, 2, 3, 12} = S({1, 2, 6, 8}).
{1, 2, 3, 21} = S({1, 2, 6, 7}).
{1, 2, 4, 5} = S({1, 2, 4, 20}).
{1, 2, 4, 6} = S({1, 2, 4, 12}).
{1, 2, 4, 8} = S({1, 2, 4, 8}).
{1, 2, 4, 12} = S({1, 2, 4, 6}).
{1, 2, 4, 20} = S({1, 2, 4, 5}).
{1, 2, 6, 7} = S({1, 2, 3, 21}).
{1, 2, 6, 8} = S({1, 2, 3, 12}).
{1, 2, 6, 9} = S({1, 2, 3, 9}).
{1, 2, 6, 12} = S({1, 2, 3, 6}).
{1, 2, 6, 15} = S({1, 2, 3, 5}).
{1, 2, 6, 24} = S({1, 2, 3, 4}).
b(1) = 1 by definition, b(2) = 1+1 as 1 has only 1 as divisor.
The divisors of b(2) are 1,2,4. So b(3) can be b(2)+1, b(2)+2 and b(2)+4.
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