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A127644 a(1)=3. a(n) is the smallest positive integer not occurring earlier in the sequence such that (sum{k=1 to n) a(k)) divides product{j=1 to n} a(j). 5
3, 6, 9, 18, 12, 16, 8, 24, 32, 34, 30, 48, 15, 1, 14, 2, 17, 11, 20, 4, 26, 7, 21, 22, 5, 27, 10, 13, 25, 40, 19, 28, 33, 37, 23, 42, 38, 44, 35, 31, 41, 29, 46, 49, 39, 50, 36, 43, 47, 45, 51, 54, 55, 53, 52, 56, 57, 62, 61, 60, 64, 68, 67, 58, 63, 70, 69, 71, 65, 77, 66, 72 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Is this a permutation of the positive integers? According to Hans Havermann, this sequence matches sequence A127562 beginning with the 104th term of each. Unlike sequence A127562, the sum of the first n terms of this sequence divides the product of the first n terms for every positive integer n.

LINKS

Table of n, a(n) for n=1..72.

MAPLE

N:= 1000: # to get a(1) to a(m-1) where a(m) is the first term > N

a[1]:= 3:

R:= {$1..N} minus {3}:

P:= 3:

S:= 3:

success:= true:

for n from 2 while success and R <> {} do

   success := false;

   for r in R do

     if type((P*r)/(S+r), integer) then

        a[n]:= r;

        nmax:= n;

        R:= R minus {r};

        success:= true;

        P:= P * r;

        S:= S + r;

        break

     fi

   od:

od:

seq(a[i], i=1..nmax); # Robert Israel, Dec 13 2014

MATHEMATICA

f[l_List] := Block[{k = 1, s = Plus @@ l, p = Times @@ l}, While[MemberQ[l, k] || Mod[k*p, k + s] > 0, k++ ]; Append[l, k]]; Nest[f, {3}, 75] (* Ray Chandler, Jan 22 2007 *)

PROG

(PARI) v=[3]; print1(3, ", "); n=1; while(n<100, p=prod(i=1, #v, v[i]); if(p*n\(vecsum(v)+n)==p*n/(vecsum(v)+n)&&!vecsearch(vecsort(v), n), v=concat(v, n); print1(n, ", "); n=0); n++) \\ Derek Orr, Dec 13 2014

CROSSREFS

Cf. A127562, A127645, A127646.

Sequence in context: A198685 A070120 A070126 * A324283 A161338 A047847

Adjacent sequences:  A127641 A127642 A127643 * A127645 A127646 A127647

KEYWORD

nonn,changed

AUTHOR

Leroy Quet, Jan 22 2007

EXTENSIONS

Extended by Ray Chandler, Jan 22 2007

STATUS

approved

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Last modified October 16 07:30 EDT 2019. Contains 328051 sequences. (Running on oeis4.)