A212184 Row n of table gives exponents >= 2 in canonical prime factorization of n-th highly composite number (A002182(n)), in nonincreasing order, or 0 if no such exponent exists.

0, 0, 2, 0, 2, 3, 2, 2, 4, 2, 3, 2, 2, 4, 3, 2, 4, 2, 3, 2, 2, 4, 3, 2, 4, 2, 3, 3, 5, 2, 4, 3, 6, 2, 4, 2, 2, 3, 2, 4, 4, 5, 2, 2, 4, 2, 3, 3, 5, 2, 4, 3, 6, 2, 4, 2, 2, 5, 3, 4, 4, 5, 2, 2, 6, 3, 4, 2, 3, 3, 5, 2, 4, 3, 6, 2, 4, 2, 2, 5, 3, 4, 4, 5, 2, 2, 6

Offset

1,3

Comments

Length of row n equals A212185(n) if A212185(n) is positive, or 1 if A212185(n) = 0.

Row n of table represents second signature of A002182(n) (cf. A212172). The use of 0 in the table to represent squarefree highly composite numbers accords with the usual OEIS practice of using 0 to represent nonexistent elements when possible. In comments, the second signature of squarefree numbers is represented as { }.

No row is repeated an infinite number of times in the table. The contrary to this would imply that at least one integer appeared in A212183 an infinite number of times - something that Ramanujan proved to be false (cf. Ramanujan link). It would be interesting to know if there is an upper bound on the number of times a row can appear.

References

Srinivasa Ramanujan, Highly composite numbers, Proc. Lond. Math. Soc. 14 (1915), 347-409; reprinted in Collected Papers, Ed. G. H. Hardy et al., Cambridge 1927; Chelsea, NY, 1962.

Links

Amiram Eldar, Table of n, a(n) for n = 1..5594 (first 1000 rows)

Achim Flammenkamp, List of the first 1200 highly composite numbers.

Srinivasa Ramanujan, Highly Composite Numbers (p. 34).

Formula

Row n is identical to row A002182(n) of table A212172.

Example

First rows read: 0; 0; 2; 0; 2; 3; 2,2; 4; 2; 3; 2,2; 4;...
12 = 2^2*3 has positive exponents 2 and 1 in its canonical prime factorization (1s are often left implicit as exponents). Only exponents that are 2 or greater appear in a number's second signature; therefore, 12's second signature is {2}.  Since 12 = A002182(5), row 5 represents the second signature {2}.

Mathematica

With[{v = Import["https://oeis.org/A002182/b002182.txt", "Table"][[;; , 2]]}, exp[n_] := Select[FactorInteger[n][[;; , 2]], # > 1 &]; exp /@ v[[1 ;; 100]] /. {} -> {0} // Flatten] (* Amiram Eldar, Jan 20 2025 *)

Crossrefs

Cf. A002182, A212172, A212182, A212183, A212185.

Sequence in context: A208295 A285721 A214292 * A371571 A033769 A333636

Adjacent sequences: A212181 A212182 A212183 * A212185 A212186 A212187

Keyword

nonn,tabf

Author

Matthew Vandermast, Jul 01 2012

Status

approved