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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A178921 Product of distances between successive distinct prime divisors of n; zero if n has only 1 distinct prime factor. 2
0, 0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 1, 0, 5, 2, 0, 0, 1, 0, 3, 4, 9, 0, 1, 0, 11, 0, 5, 0, 2, 0, 0, 8, 15, 2, 1, 0, 17, 10, 3, 0, 4, 0, 9, 2, 21, 0, 1, 0, 3, 14, 11, 0, 1, 6, 5, 16, 27, 0, 2, 0, 29, 4, 0, 8, 8, 0, 15, 20, 6, 0, 1, 0, 35, 2, 17, 4, 10, 0, 3, 0, 39, 0, 4, 12, 41, 26, 9, 0, 2, 6, 21, 28, 45, 14, 1, 0, 5, 8, 3, 0, 14, 0, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,10

COMMENTS

For n <= 41, a(n) = A049087(n).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

MATHEMATICA

f[n_] := Module[{ps}, If[n <= 1, 0, ps = Transpose[FactorInteger[n]][[1]]; Times @@ Differences[ps]]]; Table[f[n], {n, 100}] (* T. D. Noe, Aug 20 2012 *)

Array[Apply[Times, Differences@ FactorInteger[#][[All, 1]] /. {} -> 0] &, 105] (* Michael De Vlieger, Sep 10 2018 *)

PROG

(Python)

#primes = [ 2, 3, ... ]

for n in range(1, 100):

    d = n

    prev = 0

    product = 1

    for p in primes:

        if d%p==0:

            if prev:

                product *= p-prev

            while d%p==0:

                d/=p

            if d==1:

                break

            prev = p

    if prev==0:

        product = 0

    print product,

(PARI) A178921(n) = if(1>=omega(n), 0, my(ps = factor(n)[, 1], m = 1); for(i=2, #ps, m *= (ps[i]-ps[i-1])); (m)); \\ Antti Karttunen, Sep 07 2018

CROSSREFS

Cf. A081060, A049087.

Cf. also A137795.

Sequence in context: A300228 A100573 A049087 * A046665 A100574 A056100

Adjacent sequences:  A178918 A178919 A178920 * A178922 A178923 A178924

KEYWORD

nonn,easy

AUTHOR

Alex Ratushnyak, Aug 18 2012

EXTENSIONS

More terms from Antti Karttunen, Sep 07 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 17 05:59 EST 2018. Contains 317275 sequences. (Running on oeis4.)