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 A120578 Irregular array where the n-th row are the divisors, not occurring earlier in the sequence, of the sum of the terms in all previous rows. a(1)=4. 3
 4, 1, 2, 7, 14, 28, 8, 56, 3, 5, 6, 10, 12, 15, 20, 24, 30, 40, 60, 120, 31, 93, 155, 465, 13, 39, 403, 1209, 17, 169, 221, 2873, 21, 293, 879, 2051, 6153, 25, 50, 311, 622, 1555, 3110, 7775, 15550, 37, 43, 74, 86, 148, 172, 259, 301, 518, 602, 1036, 1204, 1591 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Is this sequence a permutation of the positive integers? LINKS EXAMPLE Array begins: 4 1,2 7 14 28 8,56 Now these terms add up to 120. So row 7 is the divisors of 120 which do not occur earlier in the sequence. 1,2,4 and 8 occur in earlier rows, so row 7 is (3,5,6,10,12,15,20,24,30,40,60,120). MATHEMATICA f[t_] := Flatten[Append[t, Select[Divisors[Plus @@ t], FreeQ[t, # ] &]]]; Nest[f, {4}, 12] (*Chandler*) CROSSREFS Cf. A120576, A120577, A120579. Sequence in context: A141332 A084460 A216863 * A096249 A081454 A133883 Adjacent sequences:  A120575 A120576 A120577 * A120579 A120580 A120581 KEYWORD nonn,tabf AUTHOR Leroy Quet Jun 15 2006 EXTENSIONS Extended by Ray Chandler, Jun 17 2006 STATUS approved

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