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A123886 a(0)=1. a(n) = a(n-1) + (number of earlier terms {i.e., terms a(0) through a(n-1)} that divide n). 2
1, 2, 4, 5, 8, 10, 12, 13, 17, 18, 22, 23, 27, 29, 31, 33, 37, 39, 42, 43, 48, 49, 52, 54, 59, 61, 64, 66, 69, 71, 75, 77, 81, 83, 86, 88, 93, 95, 97, 100, 106, 107, 110, 112, 116, 118, 121, 122, 128, 130, 134, 136, 141, 142, 147, 149, 153, 154, 157, 159, 165, 167, 170 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

A.H.M. Smeets, Table of n, a(n) for n = 0..20000

EXAMPLE

Among terms a(0) through a(5) there are two terms that divide 6: a(0)=1, a(1)=2. So a(6) = a(5) + 2 = 12.

MAPLE

A123886 := 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-1) mod op(i, a) = 0 then nexta := nexta +1 ; fi ; od ; a := [op(a), nexta] ; od ; RETURN(a) ; end: maxn := 100 : alist := A123886(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], # ] == 0 &]]]; Nest[f, {1}, 63] (* Ray Chandler, Oct 19 2006 *)

PROG

(Python)

a, an, la = [1], 1, 1

print(la-1, an)

while la < 63:

....dc, di = 0, 0

....while di < la:

........if la%a[di] == 0:

............dc = dc+1

........di = di+1

....an = an+dc

....la, a = la+1, a+[an]

....print(la-1, an) # A.H.M. Smeets, Jan 25 2019

CROSSREFS

Cf. A123885.

Sequence in context: A112777 A188972 A047612 * A005242 A323976 A188975

Adjacent sequences:  A123883 A123884 A123885 * A123887 A123888 A123889

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

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Last modified September 22 03:20 EDT 2021. Contains 347605 sequences. (Running on oeis4.)