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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A182861 Number of distinct prime signatures represented among the unitary divisors of A025487(n). 3
1, 2, 2, 3, 2, 4, 2, 4, 4, 2, 3, 4, 6, 2, 4, 4, 6, 2, 4, 6, 4, 5, 3, 6, 2, 4, 8, 4, 8, 4, 6, 2, 4, 8, 4, 8, 4, 4, 6, 2, 6, 4, 9, 3, 8, 4, 8, 4, 6, 6, 2, 8, 4, 6, 12, 4, 8, 4, 8, 4, 6, 6, 2, 8, 4, 10, 12, 4, 6, 8, 4, 8, 6, 8, 4, 6, 9, 6, 3, 2, 8, 4, 10, 12, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = number of members m of A025487 such that d(m^k) divides d(A025487(n)^k) for all values of k. (Here d(n) represents the number of divisors of n, or A000005(n).)

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Unitary Divisor

FORMULA

a(n) = A000005(A181820(n)).

If the canonical factorization of n into prime powers is Product p^e(p), then the formula for d(n^k) is Product_p (ek + 1). (See also A146289, A146290.)

EXAMPLE

60 has 8 unitary divisors (1, 3, 4, 5, 12, 15, 20 and 60). Primes 3 and 5 have the same prime signature, as do 12 (2^2*3) and 20 (2^2*5); each of the other four numbers listed is the only unitary divisor of 60 with its particular prime signature.  Since a total of 6 distinct prime signatures appear among the unitary divisors of 60, and since 60 = A025487(13), a(13) = 6.

CROSSREFS

Cf. A000005, A025487, A034444, A085082, A146289, A146290, A181820, A182860, A182862.

Sequence in context: A218703 A326641 A144372 * A049238 A001616 A257599

Adjacent sequences:  A182858 A182859 A182860 * A182862 A182863 A182864

KEYWORD

nonn

AUTHOR

Matthew Vandermast, Jan 14 2011

EXTENSIONS

More terms from Amiram Eldar, Jun 20 2019

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 May 11 21:35 EDT 2021. Contains 343808 sequences. (Running on oeis4.)