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A177899 Nonsquarefree numbers that are not in A177880. 0
8, 16, 24, 27, 40, 48, 54, 56, 80, 81, 88, 104, 112, 120, 125, 135, 136, 152, 162, 168, 176, 184, 189, 208, 216, 232, 240, 248, 250, 264, 270, 272, 280, 296, 297, 304, 312, 328, 336, 343, 344, 351, 368, 375, 376, 378, 405, 408, 424, 432, 440, 456, 459, 464, 472, 488, 496, 512, 513, 520, 528, 536 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..62.

FORMULA

Let B(x) be the counting function for terms not exceeding x. Then for x tends to infinity, B(x)=C*x+o(x^(0.5+eps), where C = Product_{i=p^(3^k) with prime p and k>=0}(1-1/(i^2+i+1)) - 1/zeta(2).

MAPLE

isA005836 := proc(n) convert(convert(n, base, 3), set) intersect {2} ; % = {} ; end proc:

isA177880 := proc(n) local f; for f in ifactors(n)[2]  do if not isA005836(op(2, f)) then return true; end if;  end do: return false; end proc:

isA177899 := proc(n) not numtheory[issqrfree](n) and not isA177880(n) ; end proc:

for n from 1 to 1000 do if isA177899(n) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Dec 20 2010

CROSSREFS

Cf. A177880, A013929.

Sequence in context: A137845 A046099 A033859 * A246311 A244371 A144566

Adjacent sequences:  A177896 A177897 A177898 * A177900 A177901 A177902

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Dec 15 2010

STATUS

approved

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Last modified November 20 10:09 EST 2019. Contains 329334 sequences. (Running on oeis4.)