A131981 Number of early bird numbers <= n.

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 5, 5, 6, 6, 6, 6, 6, 6, 6, 7, 8, 9, 9, 10, 10, 10, 10, 10, 10, 11, 12, 13, 14, 14, 15, 15, 15, 15, 15, 16, 17, 18, 19, 20, 20, 21, 21, 21, 21, 22, 23, 24, 25, 26, 27, 27, 28, 28, 28, 29, 30, 31, 32

Offset

1,21

Comments

a(n) = number of k such that A116700(k) <= n; a(n) = n - number of k such that A131881(k) <= n.

A131982 gives numbers n such that a(n) = n/2, or numbers n such that (number of k such that A116700(k) <= n) = (number of k such that A131881(k) <= n).

Links

Klaus Brockhaus, Table of n, a(n) for n = 1..6000

Klaus Brockhaus, Plots of A131981(n)/n at various scales

Example

There are two early bird numbers <= 21, viz. 12 and 21, hence a(21) = 2.

Prog

(JBASIC)
s$ = "" : d = 0
FOR n = 1 TO 84
sn$ = str$(n)
IF instr(s$, sn$) > 0 THEN d = d+1
s$ = s$ + sn$ : print d ; ", ";
NEXT

Crossrefs

Cf. A116700 (early bird numbers), A131881 (complement of A116700), A132133 (number of n-digit terms of 131881), A105390 (number of Rollman numbers <= n), A131982 (numbers n such that A131981(n) = n/2).

Sequence in context: A280617 A072375 A340500 * A257244 A130147 A345377

Adjacent sequences: A131978 A131979 A131980 * A131982 A131983 A131984

Keyword

nonn,base

Author

Klaus Brockhaus, Aug 15 2007

Status

approved