A123885 - OEIS

A123885

a(1)=1. a(n) = a(n-1) + (number of earlier terms {i.e., terms a(1) through a(n-1)} that divide n).

1, 2, 3, 5, 7, 10, 12, 14, 16, 20, 21, 25, 26, 30, 33, 36, 37, 40, 41, 46, 50, 52, 53, 57, 60, 63, 65, 69, 70, 76, 77, 80, 83, 85, 88, 93, 95, 97, 99, 105, 107, 113, 114, 116, 119, 122, 123, 128, 130, 136, 138, 142, 144, 147, 149, 153, 156, 158, 159, 168, 169, 171, 176

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..63.

EXAMPLE

Among terms a(1) through a(5) there are three terms that divide 6: a(1)=1, a(2)=2 and a(3)=3. So a(6) = a(5) + 3 = 10.

MAPLE

A123885 := proc(maxn) local a, nexta, n, i; a := [1]; for n from 2 to maxn do nexta := op(n-1, a); for i from 1 to n-1 do if n mod op(i, a) = 0 then nexta := nexta +1; fi; od; a := [op(a), nexta]; od; RETURN(a); end: maxn := 100 : alist := A123885(maxn) : for i from 1 to maxn do printf("%d, ", op(i, alist)); end : # R. J. Mathar, Oct 21 2006

MATHEMATICA

f[l_List] := Append[l, Last[l] + Length[Select[l, Mod[Length[l] + 1, # ] == 0 &]]]; Nest[f, {1}, 63] (* Ray Chandler, Oct 19 2006 *)

CROSSREFS

Cf. A123886.

Sequence in context: A346592 A254860 A144726 * A010062 A119565 A119592

Adjacent sequences: A123882 A123883 A123884 * A123886 A123887 A123888

KEYWORD

easy,nonn

AUTHOR

Leroy Quet, Oct 17 2006

EXTENSIONS

Extended by Ray Chandler, Oct 19 2006

More terms from R. J. Mathar, Oct 21 2006

STATUS

approved