A236837 - OEIS

%I #11 Feb 07 2014 10:45:09

%S 0,1,2,3,4,9,6,7,8,21,18,11,12,13,14,27,16,81,42,19,36,49,22,39,24,0,

%T 26,63,28,33,54,31,32,93,162,91,84,37,38,99,72,41,98,43,44,189,78,47,

%U 48,77,0,243,52,57,126,0,56,117,66,59,108,61,62,147,64,441,186,67,324,121

%N The greatest inverse of A234741: a(n) = the largest k such that A234741(k) = n, and 0 if no such k exists.

%C A234741(a(n)) = n, unless n is in A236834, in which case a(n)=0.

%C For all n, a(n) <= A234742(n). A236850 gives such k that a(k) = A234742(k).

%C If n is in A236835, a(n) > A236836(n), otherwise a(n) = A236836(n).

%C a(2^n) = 2^n.

%C a(2n) = 2*a(n).

%H Antti Karttunen, <a href="/A236837/b236837.txt">Table of n, a(n) for n = 0..8192</a>

%o (Scheme, finding the greatest inverse empirically with a naive loop. A234742 gives an absolute upper bound for any inverse of A234741):

%o (define (A236837 n) (let ((u (A234742 n))) (let loop ((i u)) (let ((k (A234741 i))) (cond ((< i n) 0) ((= k n) i) (else (loop (- i 1))))))))

%Y A236834 gives the positions of zeros.

%Y Differs from A235042 and A234742 for the first time at n=25, where a(25)=0 but A235042(25)=5 and A234742(25)=25.

%Y Cf. A236836 (the least inverse of A234741).

%Y Cf. also A236833, A236835, A234741, A236841, A236850.

%K nonn

%O 0,3

%A _Antti Karttunen_, Jan 31 2014