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 A131981 Number of early bird numbers <= n. 4
 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 (list; graph; refs; listen; history; text; internal format)
 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: A091195 A280617 A072375 * A257244 A130147 A096143 Adjacent sequences:  A131978 A131979 A131980 * A131982 A131983 A131984 KEYWORD nonn,base AUTHOR Klaus Brockhaus, Aug 15 2007 STATUS approved

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