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A277815 a(n) = the largest k < n for which A264977(k) = A264977(n), or 0 if no such k exists.

%I A277815 #7 Nov 07 2016 09:11:20
%S A277815 0,0,0,0,0,1,0,0,0,0,2,7,0,5,0,0,0,0,0,11,4,9,14,0,0,17,10,15,0,13,0,
%T A277815 0,0,0,0,19,0,25,22,3,8,29,18,23,28,21,0,0,0,0,34,27,20,37,30,47,0,33,
%U A277815 26,31,0,41,0,0,0,0,0,35,0,57,38,55,0,0,50,39,44,53,6,43,16,0,58,79,36,61,46,0,56,73,42,71,0,45,0,0,0,0,0,51
%N A277815 a(n) = the largest k < n for which A264977(k) = A264977(n), or 0 if no such k exists.
%H A277815 Antti Karttunen, <a href="/A277815/b277815.txt">Table of n, a(n) for n = 0..65537</a>
%F A277815 For all n >= 0, a(A277816(n)) = n.
%o A277815 (Scheme)
%o A277815 (define (A277815 n) (if (zero? n) n (let ((v (A264977 n))) (let loop ((k (- n 1))) (cond ((zero? k) 0) ((= v (A264977 k)) k) (else (loop (- k 1))))))))
%Y A277815 Cf. A264977, A277695, A277814, A277817 (the positions of zeros).
%Y A277815 Left inverse of A277816.
%K A277815 nonn
%O A277815 0,11
%A A277815 _Antti Karttunen_, Nov 06 2016