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 A139315 a(n) is the smallest integer k such that n*k is the smallest multiple of k with twice as many divisors as k, or 0 if no such number is possible. 4
 1, 2, 6, 12, 60, 120, 1260, 840, 0, 2520, 27720, 55440, 0, 720720, 1081080, 2162160, 61261200, 36756720, 1396755360, 2327925600, 0, 698377680, 16062686640, 48188059920, 0, 749592043200, 160626866400, 240940299600, 0, 6987268688400 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS Proof that a(10)=0. In order for 10*k to have twice as many divisors as k, it must be either a multiple of 20 but not of 40 or 100 (in which case 8*k has twice as many divisors) or a multiple of 50 but not of 100 or 250 (in which case 4*k has twice as many divisors.) In both cases, 10*k is not the smallest number with twice as many divisors as k and so a(10) of this sequence is 0. Generalizing above result, a(pq)=0 for distinct primes p,q with p

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Last modified June 13 00:57 EDT 2021. Contains 344980 sequences. (Running on oeis4.)