The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A339195 Triangle of squarefree numbers grouped by greatest prime factor, read by rows. 4
 2, 3, 6, 5, 10, 15, 30, 7, 14, 21, 35, 42, 70, 105, 210, 11, 22, 33, 55, 66, 77, 110, 154, 165, 231, 330, 385, 462, 770, 1155, 2310, 13, 26, 39, 65, 78, 91, 130, 143, 182, 195, 273, 286, 390, 429, 455, 546, 715, 858, 910, 1001, 1365, 1430, 2002, 2145, 2730, 3003, 4290, 5005, 6006, 10010, 15015, 30030 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also Heinz numbers of subsets of {1..n} that contain n, where the Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k). A019565 in its triangle form, but omitting its initial row and with each row's terms in increasing order. - Peter Munn, Feb 26 2021 LINKS FORMULA For n > 1, T(n,k) = prime(n) * A261144(n-1,k). EXAMPLE Triangle begins:    2    3   6    5  10  15  30    7  14  21  35  42  70  105  210 MATHEMATICA Table[Prime[n]*Sort[Times@@Prime/@#&/@Subsets[Range[n-1]]], {n, 5}] CROSSREFS A000079 (shifted left) gives row lengths. A339360 gives row sums. A000040 is column k = 1. A100484 is column k = 2. A001748 is column k = 3. A002110 is column k = 2^(n-1). A070826 is column k = 2^(n-1) - 1. A209862 takes prime indices to binary indices in these terms. A246867 groups squarefree numbers by Heinz weight, with row sums A147655. A261144 divides the n-th row by prime(n), with row sums A054640. A339116 is the restriction to semiprimes, with row sums A339194. A005117 lists squarefree numbers, ordered lexicographically by prime factors: A019565. A006881 lists squarefree semiprimes. A072047 counts prime factors of squarefree numbers. A319246 is the sum of prime indices of the n-th squarefree number. A329631 lists prime indices of squarefree numbers, reversed: A319247. A338899/A270650/A270652 give the prime indices of squarefree semiprimes. Cf. A001221, A014342, A014466, A098350, A112798, A320656, A326882, A338901. Sequence in context: A073740 A239956 A077320 * A019565 A309840 A340316 Adjacent sequences:  A339192 A339193 A339194 * A339196 A339197 A339198 KEYWORD nonn,tabf AUTHOR Gus Wiseman, Dec 02 2020 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 6 14:16 EDT 2021. Contains 343586 sequences. (Running on oeis4.)