LINKS
Robert G. Wilson v and Sean A. Irvine, <a href="/A003681/b003681_2.txt">Table of n, a(n) for n = 1..19</a> [a(19) added by Sean A. Irvine, Jul 29 2015.]
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Revision History for A003681
(Bold, blue-underlined text is an addition; faded, red-underlined text is aShowing entries 1-10 | older changes
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approved
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NAME
a(n) = min { p +- q : p +- q > 1 : pq and p*q = Product_{k=1..n-1} a(k) }.
COMMENTS
The + sign in the definition applies only for n = 1 and n = 2, thereafter only the - sign is relevant and will yield the minimum. - M. F. Hasler, Aug 17 2015
PROG
(PARI) A003681(N, a=[2, 3])={while(#a<N, my(d=divisors(prod(i=1, #a, a[i]))); for(i=(#d)\2, #d, d[i+1]-d[#d-i]>1||next; a=concat(a, d[i+1]-d[#d-i]); break)); a} \\ May require allocatemem() for N >= 15. - M. F. Hasler, Aug 17 2015
NAME
a(n) = min ( { p +- q > 1 : pq = product_Product_{k=1..n-1} a(k)) }.
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reviewed
editing
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reviewed
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editing
proposed
COMMENTS
a(n) = A082120(Product_{k=1..n-1} a(k)) for n >= 3. - Robert Israel, Aug 12 2015
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proposed
editing