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A076643 Positive integers read backwards, but omit a number if it is <= an earlier number. 1
1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 21, 31, 41, 51, 61, 71, 81, 91, 92, 93, 94, 95, 96, 97, 98, 99, 101, 201, 301, 401, 501, 601, 701, 801, 901, 911, 921, 931, 941, 951, 961, 971, 981, 991, 992, 993, 994, 995, 996, 997, 998, 999, 1001, 2001, 3001, 4001, 5001, 6001, 7001 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n+1) - a(n) is a power of 10 or 2 if a(n) is of the form 10^m - 1. - David A. Corneth, Nov 26 2018

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

FORMULA

a((9*m^2 + 7*m + 2) / 2) = 10^m - 1, m > 0. - David A. Corneth, Nov 25 2018

EXAMPLE

The beginning list is 1,2,3,4,5,6,7,8,9,1,11; but 1 < 9 so omit it.

MAPLE

d := N->`if`(N=0, [0], ListTools[Reverse](convert(N, base, 10))); a := N->sum(d(N)[n]*10^(n-1), n=1..nops(d(N))); dropsort := proc(S)::list; description "Forms a strictly increasing list by dropping terms."; local T, V; T := k->max(seq(S[j], j=1..k)); V := ListTools[MakeUnique]([seq(T(j), j=1..nops(S))]); return(V); end proc; dropsort([seq(a(n), n=1..2000)]);

MATHEMATICA

Union@ FoldList[Max, IntegerReverse@ Range@ 1007] (* Michael De Vlieger, Nov 25 2018 *)

PROG

(PARI) nxt(n) = {my(d = digits(n), i = 1); while(i <= #d && d[i] == 9, i++); if(i <= #d, n+10^(#d-i), n+2)}

first(n) = my(res = vector(n)); res[1] = 1; for(i = 2, n, res[i] = nxt(res[i-1])); res \\ David A. Corneth, Nov 25 2018

CROSSREFS

Cf. A004086.

Sequence in context: A096106 A321990 A076641 * A352463 A326402 A127204

Adjacent sequences:  A076640 A076641 A076642 * A076644 A076645 A076646

KEYWORD

nonn,easy,look,base

AUTHOR

Francois Jooste (phukraut(AT)hotmail.com), Oct 23 2002

STATUS

approved

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Last modified May 17 19:51 EDT 2022. Contains 353778 sequences. (Running on oeis4.)