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%I #8 Nov 16 2017 15:52:24
%S 576,584,588,592,600,1650,1654,3430,3440,3448,3452,3458,3462,3466,
%T 3474,3520,3600,3608,3610
%N Numbers n such that A131981(n) = n/2.
%C Numbers n such that number of terms <= n of A116700 equals number of terms <= n of A131881.
%C Numbers n such that numbers of numbers that occur in the concatenation of 1,2,3...,n-1 equals numbers of numbers that do not occur in the concatenation of 1,2,3...,n-1.
%C There are no other terms <= 600000. The plots in the link strongly suggest that the sequence is complete.
%H Klaus Brockhaus, <a href="/A131981/a131981.gif">Plots of A131981(n)/n at various scales</a>
%e A131981(n) < n/2 for 1 <=n < 576,
%e A131981(n) < n/2 for 576 < n < 584,
%e A131981(n) > n/2 for 584 < n < 588,
%e A131981(n) < n/2 for 588 < n < 592,
%e A131981(n) > n/2 for 592 < n < 600,
%e A131981(n) > n/2 for 600 < n < 1650,
%e A131981(n) > n/2 for 1650 < n < 1654,
%e A131981(n) < n/2 for 1654 < n < 3430,
%e A131981(n) > n/2 for 3430 < n < 3440,
%e ..............
%e A131981(n) < n/2 for 3608 < n <= 3610,
%e A131981(n) > n/2 for 3610 < n <= 600000.
%o (JBASIC)
%o s$ = "" : c = 0 : d = 0
%o FOR n = 1 TO 4000
%o sn$ = str$(n)
%o IF instr(s$, sn$) > 0 THEN d = d+1 ELSE c = c+1
%o s$ = s$ + sn$ : IF c = d THEN print n ; ",";
%o NEXT
%Y Cf. A116700 (early bird numbers), A131881 (complement of A116700), A131981 (number of early bird numbers <= n), A105390 (number of Rollman numbers <= n), A105391 (numbers n such that A105390(n) = n/2).
%K nonn,base
%O 1,1
%A _Klaus Brockhaus_, Aug 15 2007
%E Edited by _Charles R Greathouse IV_, Oct 28 2009
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