A068191 - OEIS

%I #30 Sep 16 2024 14:26:10

%S 11,13,17,19,22,23,26,29,31,33,34,37,38,39,41,43,44,46,47,51,52,53,55,

%T 57,58,59,61,62,65,66,67,68,69,71,73,74,76,77,78,79,82,83,85,86,87,88,

%U 89,91,92,93,94,95,97,99,101,102,103,104,106,107,109,110,111,113,114

%N Numbers n such that A067734(n)=0; complement of A002473; at least one prime-factor of n is larger than 7, it has 2 decimal digits.

%C Also numbers n such that A198487(n) = 0 and A107698(n) = 0. - _Jaroslav Krizek_, Nov 04 2011

%C A086299(a(n)) = 0. - _Reinhard Zumkeller_, Apr 01 2012

%C A262401(a(n)) < a(n). - _Reinhard Zumkeller_, Sep 25 2015

%C Numbers not in A007954. - _Mohammed Yaseen_, Sep 13 2022

%H Reinhard Zumkeller, <a href="/A068191/b068191.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range@120, Last@Map[First, FactorInteger@#] > 7 &] (* _Vincenzo Librandi_, Sep 19 2016 *)

%o (Haskell)

%o import Data.List (elemIndices)

%o a068191 n = a068191_list !! (n-1)

%o a068191_list = map (+ 1) $ elemIndices 0 a086299_list

%o -- _Reinhard Zumkeller_, Apr 01 2012

%o (Python)

%o from sympy import integer_log

%o def A068191(n):

%o     def f(x):

%o         c = n

%o         for i in range(integer_log(x,7)[0]+1):

%o             i7 = 7**i

%o             m = x//i7

%o             for j in range(integer_log(m,5)[0]+1):

%o                 j5 = 5**j

%o                 r = m//j5

%o                 for k in range(integer_log(r,3)[0]+1):

%o                     c += (r//3**k).bit_length()

%o         return c

%o     m, k = n, f(n)

%o     while m != k: m, k = k, f(k)

%o     return m # _Chai Wah Wu_, Sep 16 2024

%Y Cf. A001222, A002473, A067734.

%Y Cf. A068183, A068184, A068185, A068186, A068187, A068189, A068190.

%Y Cf. A262401.

%K base,nonn,changed

%O 1,1

%A _Labos Elemer_, Feb 19 2002