a(n) = product of distinct primes of form 4k-1 that divide n.
1, 1, 3, 1, 1, 3, 7, 1, 3, 1, 11, 3, 1, 7, 3, 1, 1, 3, 19, 1, 21, 11, 23, 3, 1, 1, 3, 7, 1, 3, 31
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Thu Dec 24 07:42:43 CET 2009 [seqfan] Analogue of A170818; Product of distinct primes of the form 6n+1 (A002476 ) dividing n.