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 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

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