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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A180484 Numbers n such that r*(n/k)^2 is an integer. n=(x_1 x_2 ... x_r) where x_i are digits of n, k = x_1 * x_2 * ... * x_r. 2
1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 15, 24, 36, 111, 112, 115, 128, 132, 135, 144, 175, 212, 216, 224, 312, 315, 384, 432, 612, 624, 672, 735, 816, 1111, 1112, 1113, 1114, 1115, 1116, 1121, 1122, 1124, 1125, 1127, 1128, 1131, 1134, 1144, 1161, 1164, 1176, 1184 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A007602 is a subsequence, with 1114 the first nonmember of A007602. [D. S. McNeil, Sep 09 2010]

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..19985

EXAMPLE

n=36, r=2, 2*(36/3*6)^2=8, n=36 belongs to the sequence.

MAPLE

A055642 := proc(n) max(1, ilog10(n)+1) ; end proc:

A007954 := proc(n) mul(d, d= convert(n, base, 10)) : end proc:

isA180484 := proc(n) r := A055642(n) ; k := A007954(n) ; if k <> 0 then type(r*n^2/k^2, 'integer') ; else false; end if; end proc:

for n from 1 to 2200 do if isA180484(n) then printf("%d, ", n) ; end if; end do:

# R. J. Mathar, Sep 08 2010

PROG

(Python)

from gmpy2 import t_mod, mpz

from operator import mul

from functools import reduce

A180484 = [mpz(n) for n in (str(x) for x in range(1, 10**9)) if not

..........(n.count('0') or t_mod(mpz(n)**2*len(n),

..........reduce(mul, (mpz(d) for d in n))**2))]

# Chai Wah Wu, Aug 26 2014

CROSSREFS

Cf. A007602

Sequence in context: A209933 A182183 A064700 * A007602 A167620 A169935

Adjacent sequences:  A180481 A180482 A180483 * A180485 A180486 A180487

KEYWORD

base,easy,nonn

AUTHOR

Ctibor O. Zizka, Sep 07 2010

EXTENSIONS

More terms from R. J. Mathar and D. S. McNeil, Sep 08 2010

Updated an A-number in a comment R. J. Mathar, Oct 18 2010

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 20 03:10 EDT 2019. Contains 323412 sequences. (Running on oeis4.)