|
| |
|
|
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.
|
|
3
|
|
|
|
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
|
Table of n, a(n) for n=1..100.
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}]]
|
|
|
PROG
|
(Haskell)
a302170 n k = a302170_tabl !! (n-1) !! (k-1)
a302170_tabl = map a302170_row [1..]
a302170_row = reverse . a027748_row
-- Brian Chess, Sep 19 2022
|
|
|
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
|
| |
|
|
