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 A136193 Irregular array read by rows: row n contains the products of each pair of consecutive positive divisors of n. 1
 2, 3, 2, 8, 5, 2, 6, 18, 7, 2, 8, 32, 3, 27, 2, 10, 50, 11, 2, 6, 12, 24, 72, 13, 2, 14, 98, 3, 15, 75, 2, 8, 32, 128, 17, 2, 6, 18, 54, 162, 19, 2, 8, 20, 50, 200, 3, 21, 147, 2, 22, 242, 23, 2, 6, 12, 24, 48, 96, 288, 5, 125, 2, 26, 338, 3, 27, 243 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS The first listed row is row 2. Row n contains d(n)-1 (= A032741(n)) terms, where d(n) is the number of positive divisors of n. LINKS EXAMPLE The positive divisors of 20 are 1,2,4,5,10,20. 1*2=2. 2*4=8. 4*5=20. 5*10=50. 10*20=200. So row 20 is (2,8,20,50,200). The first few rows of the triangle are: 2; 3; 2, 8; 5; 2, 6, 18; 7; 2, 8, 32; ... MAPLE with(numtheory): a:=proc(n) local div: div:=divisors(n): seq(div[j]*div[j+1], j=1..tau(n)-1) end proc: for n from 2 to 25 do a(n) end do; # yields sequence as a two-dimensional array - Emeric Deutsch, Jan 08 2008 MATHEMATICA Flatten[Table[Times@@@Partition[Divisors[n], 2, 1], {n, 30}]]  (* Harvey P. Dale, Apr 23 2011 *) PROG (PARI) tabf(nn) = {for (n = 2, nn, d = divisors(n); for (i = 1, #d - 1, print1(d[i]*d[i+1], ", "); ); ); } \\ Michel Marcus, Feb 10 2014 CROSSREFS Cf. A032741, A078730, A136195, A136181. Sequence in context: A063708 A096488 A011280 * A187789 A245922 A098513 Adjacent sequences:  A136190 A136191 A136192 * A136194 A136195 A136196 KEYWORD nonn,tabf AUTHOR Leroy Quet, Dec 20 2007; corrected Jan 20 2008 EXTENSIONS More terms from Emeric Deutsch, Jan 08 2008 More terms from Michel Marcus, Feb 10 2014 STATUS approved

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Last modified September 23 02:26 EDT 2021. Contains 347609 sequences. (Running on oeis4.)