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 A302170 Irregular triangle T(n,k) read by rows: first row is 1, n-th row (n > 1) lists distinct prime factors of n in decreasing order. 1
 1, 2, 3, 2, 5, 3, 2, 7, 2, 3, 5, 2, 11, 3, 2, 13, 7, 2, 5, 3, 2, 17, 3, 2, 19, 5, 2, 7, 3, 11, 2, 23, 3, 2, 5, 13, 2, 3, 7, 2, 29, 5, 3, 2, 31, 2, 11, 3, 17, 2, 7, 5, 3, 2, 37, 19, 2, 13, 3, 5, 2, 41, 7, 3, 2, 43, 11, 2, 5, 3, 23, 2, 47, 3, 2, 7, 5, 2, 17, 3, 13, 2, 53, 3, 2, 11, 5, 7, 2, 19, 3, 29, 2, 59, 5, 3, 2, 61, 31, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Eric Weisstein's World of Mathematics, Distinct Prime Factors FORMULA T(n,1) = A006530(n). T(n,A001221(n)) = A020639(n). EXAMPLE The irregular triangle begins: 1:  {1} 2:  {2} 3:  {3} 4:  {2} 5:  {5} 6:  {3, 2} 7:  {7} 8:  {2} 9:  {3} 10: {5, 2} 11: {11} 12: {3, 2} MATHEMATICA Flatten[Table[Reverse[FactorInteger[n][[All, 1]]], {n, 1, 62}]] CROSSREFS Cf. A001221 (row lengths), A006530, A008472 (row sums), A020639, A027746, A027748 (аnother version), A027750, A056538, A085307, A238689. Sequence in context: A112764 A108728 A331962 * A049805 A104887 A064886 Adjacent sequences:  A302167 A302168 A302169 * A302171 A302172 A302173 KEYWORD nonn,tabf AUTHOR Ilya Gutkovskiy, Apr 02 2018 STATUS approved

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Last modified September 23 15:43 EDT 2020. Contains 337310 sequences. (Running on oeis4.)