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

 

Logo

"Email this user" was broken Aug 14 to 9am Aug 16. If you sent someone a message in this period, please send it again.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A068186 a(n) is the largest number whose product of decimal digits equals n^n. 1
22, 333, 22222222, 55555, 333333222222, 7777777, 222222222222222222222222, 333333333333333333, 55555555552222222222, 0, 333333333333222222222222222222222222, 0, 7777777777777722222222222222 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

No digit=1 is permitted to avoid infinite number of solutions; a(n)=0 if A067734(n^n)=0.

LINKS

Chai Wah Wu, Table of n, a(n) for n = 2..100

FORMULA

a(n) is obtained as prime factors of n^n concatenated in order of magnitude and with repetitions; a(n)=0 if n has p > 7 prime factors.

EXAMPLE

n=10, 10^10=10000000000, a(5)=55555555552222222222.

PROG

(Python)

from sympy import factorint

def A068186(n):

    if n == 1:

        return 1

    pf = factorint(n)

    ps = sorted(pf.keys(), reverse=True)

    if ps[0] > 7:

        return 0

    s = ''

    for p in ps:

        s += str(p)*(n*pf[p])

    return int(s) # Chai Wah Wu, Aug 12 2017

CROSSREFS

Cf. A000312, A001222, A002473, A067734, A068183-A068187, A068189-A068191.

Sequence in context: A000461 A216730 A048795 * A021284 A019623 A021794

Adjacent sequences:  A068183 A068184 A068185 * A068187 A068188 A068189

KEYWORD

base,nonn,changed

AUTHOR

Labos Elemer, Feb 19 2002

EXTENSIONS

a(12) corrected by Chai Wah Wu, Aug 12 2017

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 August 17 15:07 EDT 2017. Contains 290635 sequences.