A200780 a(n) = number of i in the range 1 <= i <= n such that b(i)=b(n), where b is the sequence A181391 taken with offset 1.

1, 2, 1, 3, 1, 4, 2, 3, 2, 1, 5, 1, 6, 4, 2, 2, 1, 7, 3, 1, 8, 2, 5, 1, 9, 2, 2, 3, 3, 1, 10, 4, 4, 4, 1, 11, 5, 5, 6, 6, 1, 12, 5, 1, 13, 6, 1, 14, 7, 8, 3, 1, 15, 7, 2, 1, 16, 3, 1, 17, 9, 2, 1, 18, 4, 1, 19, 10, 2, 11, 7, 1, 20, 6, 2, 12, 7, 13, 8, 2, 1, 21, 3, 1, 22, 14, 3, 3, 1, 23, 8, 1, 24, 15, 4, 5, 4

Offset: 1

Author

N. J. A. Sloane, Nov 22 2011

Keywords

• nonn

Comments

Equivalently, this is the ORDINAL transform of Van Eck's sequence A181391. - N. J. A. Sloane, Apr 09 2020

Links

• Rémy Sigrist, Table of n, a(n) for n = 1..10000
• Rémy Sigrist, C++ program for A200780

Crossrefs

Cf. A181391.

Programs

Maple

# The ORDINAL transform of a sequence a[0], a[1], a[2], ... is the sequence b[0], b[1], b[2], ... where b[n] is the number of times a[n] has occurred in [a[0], ..., a[n]].
ORDINAL:=proc(a)  local b,t1,tlist,clist,n,t,nt;
if whattype(a) <> list then RETURN([]); fi:
t1:=nops(a);
tlist:=[];
clist:=Array(1..t1,0);
b:=[]; nt:=0;
for n from 1 to t1 do t:=a[n];
if member(t,tlist,'p') then clist[p] := clist[p]+1; b:=[op(b),clist[p]];
else nt:=nt+1; tlist:=[op(tlist),t]; clist[nt]:=1; b:=[op(b),1]; fi;
od: b; end: # N. J. A. Sloane, Apr 09 2020
See also A200779.