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A009996 Numbers with digits in nonincreasing order. 20
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 20, 21, 22, 30, 31, 32, 33, 40, 41, 42, 43, 44, 50, 51, 52, 53, 54, 55, 60, 61, 62, 63, 64, 65, 66, 70, 71, 72, 73, 74, 75, 76, 77, 80, 81, 82, 83, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 110, 111, 200, 210, 211 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Base 10 representation Sum{d(i)*10^i: i=0,1,...,m} has d(m) >= d(m-1) >= ... >= d(1) >= d(0).

These numbers might be called "Nialpdromes".

A004186(a(n)) = a(n). - Reinhard Zumkeller, Oct 31 2007

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..1000

D. Applegate, M. LeBrun, N. J. A. Sloane, Dismal Arithmetic, J. Int. Seq. 14 (2011) # 11.9.8.

David A. Corneth, Table of n, a(n) for n = 1..20000, Jun 03 2014

Eric Weisstein's World of Mathematics, Digit

FORMULA

Binomial(n+k,k) = (n+k)!/(n!*k!). d(i) is the i-th digit of a(n). q is the number of digits of a(n). Find the highest m such that C(10 + m, 10) - m + 1 <= n. a(n) has m+1 digits. Set n = n - C(10+m,10). Find the highest d(m+1), then d(m), then ..., then d(1) each iteration such that C(d(m+1)+m+1,1+m+1)<=n. Then set n = n-C(d(m+1)+m+1,m+2). If n = 0 then stop. All remaining digits are 0.

EXAMPLE

As 10000 = C(10+6,10) - 6 + C(7+6,1+6) + C(5+5,1+5) + C(4+4,1+4) + C(3+3,1+3) + C(1+2,1+2) + C(0+1,1+1), C(0+0,1+0), a(10000) = 7543100.

MATHEMATICA

Select[Range[0, 211], GreaterEqual@@IntegerDigits[#]&] (* Ray Chandler, Oct 25 2011 *)

PROG

(PARI) is(n)=my(d=digits(n)); for(i=2, #d, if(d[i]>d[i-1], return(0))); 1 \\ Charles R Greathouse IV, Jan 02 2014

(PARI) \\ This program is optimized for fast calculation of a(n) for large n.

a(n)={my(q, m=10, i, r=0); n--; while(binomial(m+1, 10)<=n+m-9, m++); n-=binomial(m, 10); n+=m-9; q=m-9; i=q; while(n>0, m=i; while(binomial(m+1, i)<=n, m++); r=10*r+m+1-i; n-=binomial(m, i); i--; ); z=q-#digits(r); r*=10^z; r} \\ David A. Corneth, Jun 01 2014

(PARI) \\recursive--feed an element a(n)>0 and it gives a(n+1).

nxt(n)={my(r, d=digits(n), y, t); if(d[#d]!=9, y=1; while(y-#d-1&&d[y]==9, y++); t=#d; forstep(i=t, y+1, -1, if(d[i-1]!=d[i], t=i-1; break)); if(t!=#d, d[t+1]++; for(i=t+2, #d, d[i]=0), d[y]++; for(i=y+1, #d, d[i]=0)); r=d , d=vector(#d+1); d[1]=1; for(i=2, #d, d[i]=0); r=d); sum(i=1, #r, 10^(#r-i)*r[i])} \\ David A. Corneth, Jun 01 2014

CROSSREFS

Differs from A032873 and A032907.

Cf. A064222, A152054.

Sequence in context: A084383 A032873 A072543 * A032907 A130576 A190220

Adjacent sequences:  A009993 A009994 A009995 * A009997 A009998 A009999

KEYWORD

nonn,base,look

AUTHOR

N. J. A. Sloane

EXTENSIONS

Corrected by Rick L. Shepherd, Jun 06 2002

STATUS

approved

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Last modified October 18 08:56 EDT 2017. Contains 293506 sequences.