a(n) is the least k that has exactly n proper divisors d such that (-d)^k == -d (mod k).

Terms

a(0) =1a(1) =2a(2) =6a(3) =42a(4) =66a(5) =105a(6) =2805a(7) =561a(8) =1365a(9) =5005a(10) =5565a(11) =11305a(12) =36465a(13) =140505a(14) =239785a(15) =41041a(16) =682465a(17) =873145a(18) =185185a(19) =418285a(20) =1683969a(21) =2113665a(22) =5503785a(23) =1242241a(24) =6697405a(25) =8549905a(26) =31932901a(27) =11996985a(28) =31260405a(29) =30534805