login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A304038 Irregular triangle T(n,k) read by rows: first row is 0, n-th row (n > 1) lists indices of distinct primes dividing n. 1
0, 1, 2, 1, 3, 1, 2, 4, 1, 2, 1, 3, 5, 1, 2, 6, 1, 4, 2, 3, 1, 7, 1, 2, 8, 1, 3, 2, 4, 1, 5, 9, 1, 2, 3, 1, 6, 2, 1, 4, 10, 1, 2, 3, 11, 1, 2, 5, 1, 7, 3, 4, 1, 2, 12, 1, 8, 2, 6, 1, 3, 13, 1, 2, 4, 14, 1, 5, 2, 3, 1, 9, 15, 1, 2, 4, 1, 3, 2, 7, 1, 6, 16, 1, 2, 3, 5, 1, 4, 2, 8, 1, 10, 17, 1, 2, 3, 18, 1, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..100.

Eric Weisstein's World of Mathematics, Distinct Prime Factors

Index entries for sequences computed from indices in prime factorization

FORMULA

T(n,k) = A000720(A027748(n,k)).

T(n,1) = A055396(n).

T(n,A001221(n)) = A061395(n).

EXAMPLE

The irregular triangle begins:

1:  {0}

2:  {1}

3:  {2}

4:  {1}

5:  {3}

6:  {1, 2}

7:  {4}

8:  {1}

9:  {2}

10: {1, 3}

11: {5}

12: {1, 2}

MATHEMATICA

Flatten[Table[PrimePi[FactorInteger[n][[All, 1]]], {n, 1, 62}]]

CROSSREFS

Cf. A000040, A000720, A001221 (row lengths), A027748, A055396, A061395, A066328 (row sums), A112798, A156061 (row products), A302170.

Sequence in context: A089384 A228812 A144113 * A301983 A165416 A222818

Adjacent sequences:  A304035 A304036 A304037 * A304039 A304040 A304041

KEYWORD

nonn,tabf

AUTHOR

Ilya Gutkovskiy, May 05 2018

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 24 22:26 EDT 2019. Contains 322446 sequences. (Running on oeis4.)