1,1

Numbers n such that number of terms <= n of A116700 equals number of terms <= n of A131881.

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.

There are no other terms <= 600000. The plots in <a href="http://www.research.att.com/~njas/sequences/a131981.gif">a131981.gif</a> strongly suggest that the sequence is finite and full.

A131981(n) < n/2 for 1 <=n < 576,

A131981(n) < n/2 for 576 < n < 584,

A131981(n) > n/2 for 584 < n < 588,

A131981(n) < n/2 for 588 < n < 592,

A131981(n) > n/2 for 592 < n < 600,

A131981(n) > n/2 for 600 < n < 1650,

A131981(n) > n/2 for 1650 < n < 1654,

A131981(n) < n/2 for 1654 < n < 3430,

A131981(n) > n/2 for 3430 < n < 3440,

..............

A131981(n) < n/2 for 3608 < n <= 3610,

A131981(n) > n/2 for 3610 < n <= 600000.

(JBASIC)

s$ = "" : c = 0 : d = 0

FOR n = 1 TO 4000

sn$ = str$(n)

IF instr(s$, sn$) > 0 THEN d = d+1 ELSE c = c+1

s$ = s$ + sn$ : IF c = d THEN print n ; ", ";

NEXT

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).

Sequence in context: A027527 A069421 A136111 this_sequence A053969 A109101 A064253

Adjacent sequences: A131979 A131980 A131981 this_sequence A131983 A131984 A131985

nonn,base

Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Aug 15 2007