A357030 - OEIS

%I #56 Mar 04 2024 08:51:20

%S 1,2,3,4,5,6,7,8,9,10,11,12,12,12,12,12,12,12,12,12,13,14,15,15,15,15,

%T 15,15,15,15,16,17,18,19,19,19,19,19,19,19,20,21,22,23,24,24,24,24,24,

%U 24,25,26,27,28,29,30,30,30,30,30,31,32,33,34,35,36,37,37,37,37,38,39,40

%N a(n) is the number of integers in 0..n having nonincreasing digits.

%e a(20) = 13 because there are 13 numbers in 0..20 whose digits are in nonincreasing order: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 20.

%p a:= proc(n) option remember; `if`(n<0, 0, a(n-1)+`if`(

%p      (l-> is(l=sort(l)))(convert(n, base, 10)), 1, 0))

%p     end:

%p seq(a(n), n=0..72);  # _Alois P. Heinz_, Sep 12 2022

%t Accumulate @ Table[If[GreaterEqual @@ IntegerDigits[n], 1, 0], {n, 0, 72}] (* _Amiram Eldar_, Sep 10 2022 *)

%o (PARI) a(n) = sum(k=0, n, my(d=digits(k)); d == vecsort(d,,4)); \\ _Michel Marcus_, Sep 10 2022

%Y Cf. A009996.

%K nonn,base

%O 0,2

%A _Osman Mustafa Quddusi_, Sep 09 2022