OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
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
MATHEMATICA
Select[Range[500], AnyTrue[(e = FactorInteger[#][[;; , 2]]), #1 > 1 &] && AllTrue[e, DigitCount[#1, 3, 2] == 0 &] &] (* Amiram Eldar, Aug 31 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Dec 15 2010
STATUS
approved