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 A247654 Write 4n as a product of numbers of the form 4k+2 (A016825) so as to minimize the sum of the factors; a(n) is this sum. 2
 4, 6, 8, 8, 12, 10, 16, 10, 12, 14, 24, 12, 28, 18, 16, 12, 36, 14, 40, 16, 20, 26, 48, 14, 20, 30, 24, 20, 60, 18, 64, 14, 28, 38, 24, 16, 76, 42, 32, 18, 84, 22, 88, 28, 28, 50, 96, 16, 28, 22, 40, 32, 108, 18, 32, 22, 44, 62, 120, 20, 124, 66, 32, 16, 36 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Suggested by reading Joshua Zucker's puzzle in Gary Antonick's Numberplay column for April 22 2013. LINKS Jens Kruse Andersen, Table of n, a(n) for n = 1..10000 Gary Antonick, The Primes in Evenland Puzzle, Numberplay Column, Wordplay Blog, New York Times, April 22, 2013 EXAMPLE 20 = 2*10 so a(5) = 2+10 = 12. The first time there is a choice is when n=9: 36 = 2*18 = 6*6, and the latter gives the smaller sum, so a(9) = 6+6 = 12. PROG (PARI) f(x, i)=local(t); if(x==1, 0, if(i>#d, 2^99, t=f(x, i+1); if(x%d[i], t, min(t, d[i]+f(x/d[i], i))))) a(n)=d=select(m->m%4==2, divisors(4*n)); f(4*n, 1) \\ Jens Kruse Andersen, Oct 01 2014 CROSSREFS Cf. A016825, A001414. A bisection of A247653. Sequence in context: A027709 A196358 A079775 * A262767 A104173 A023991 Adjacent sequences:  A247651 A247652 A247653 * A247655 A247656 A247657 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 30 2014 EXTENSIONS Definition corrected and more terms from Jens Kruse Andersen, Oct 01 2014 STATUS approved

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Last modified June 18 20:45 EDT 2021. Contains 345121 sequences. (Running on oeis4.)