Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 4500 articles have referenced us, often saying "we would not have discovered this result without the OEIS".
Table of n, a(n) for n=1..57.
At n=10, he C(10,5) = 252=4*9*7 has 18 divisors, 8 are unitary and the residual 10 are non-unitary; thus a[ 10 ]=10=18-8.
A048105 applied to terms of A001405.
Sequence in context: A197007 A011449 A231037 * A159814 A169774 A057611
Adjacent sequences: A048240 A048241 A048242 * A048244 A048245 A048246