A340377 - OEIS

%I #13 Jan 16 2021 06:39:02

%S 1,3,5,9,13,17,19,21,35,47,53,59,67,71,73,91,93,95,121,123,129,143,

%T 145,157,163,173,175,179,207,211,229,233,239,255,267,291,297,299,321,

%U 327,351,355,371,381,405,413,437,451,477,479,485,487,499,503,505,523,527,541,547,549,557,595,643,645,647,661,691,701

%N Numbers k such that there are no 2-digits in the ternary expansion of A048673(k).

%C All terms are odd, because A048673(2n) = 3*A048673(n) - 1, which forces the least significant digit in the ternary expansion of A048673(2n) to be "2".

%H Antti Karttunen, <a href="/A340377/b340377.txt">Table of n, a(n) for n = 1..20000</a>

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

%o (PARI)

%o A003961(n) = my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); \\ From A003961

%o A048673(n) = (A003961(n)+1)/2;

%o A289814(n) = { my (d=digits(n, 3)); fromdigits(vector(#d, i, if (d[i]==2, 1, 0)), 2); } \\ From A289814

%o A291759(n) = A289814(A048673(n));

%o isA340377(n) = (0==A291759(n));

%Y Positions of zeros in A291759 and in A340379. Positions of ones in A340382.

%Y Cf. A048673, A340376.

%K nonn

%O 1,2

%A _Antti Karttunen_, Jan 15 2021