OFFSET
1,2
COMMENTS
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 = [int(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
(PARI) is(n)=my(d=digits(n), r=#d, k=vecprod(d)); k && denominator((n/k)^2*r)==1 \\ Charles R Greathouse IV, Jun 03 2020
CROSSREFS
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