0,4

A perfect partition of n is one which contains just one partition of every number less than n when repeated parts are regarded as indistinguishable. Thus 1^n is a perfect partition for every n; and for n = 7, 4 1^3, 4 2 1, 2^3 1 and 1^7 are all perfect partitions. [Riordan]

Also number of ordered factorizations of n+1, see A074206.

Also number of gozinta chains from 1 to n (see A034776) [ David W. Wilson ]

a(n) is the permanent of the n X n matrix with (i,j) entry = 1 if j|i+1 and = 0 otherwise. For n=3 the matrix is {{1, 1, 0}, {1, 0, 1}, {1, 1, 0}} with permanent = 2. - David Callan (callan(AT)stat.wisc.edu), Oct 19 2005

Appears to be the number of permutations that contribute to the determinant that gives the moebius function. Verified up to a(9). [From Mats O. Granvik (mgranvik(AT)abo.fi), Sep 13 2008]

Dirichlet inverse of A153881. [From Mats Granvik (mats.granvik(AT)abo.fi), Jan 03 2009]

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 126, see #27.

R. Honsberger, Mathematical Gems III, M.A.A., 1985, p. 141.

HoKyu Lee, Double perfect partitions, Discrete Math., 306 (2006), 519-525.

P. A. MacMahon, The theory of perfect partitions and the compositions of multipartite numbers, Messenger Math., 20 (1891), 103-119.

J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, pp. 123-124.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n = 0..9999

Daniele A. Gewurz and Francesca Merola, Sequences realized as Parker vectors ..., J. Integer Seqs., Vol. 6, 2003.

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Eric Weisstein's World of Mathematics, Dirichlet Series Generating Function

Index entries for "core" sequences

a(n) = sum of all a(i) such that i divides n and i < n (Clark Kimberling).

a(p^k)=2^(k-1).

a(n) = A067824(n)/2 for n>1; a(A122408(n)) = A122408(n)/2. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 03 2006

a(n-1) = sum of all a(i-1) such that i divides n and i < n. a(p^k-1)=2^(k-1). a(n-1) = A067824(n)/2 for n > 1; a(A122408(n)-1) = A122408(n)/2. - David Wasserman (dwasserm(AT)earthlink.net), Nov 14 2006

a := array(1..150): for k from 1 to 150 do a[k] := 0 od: a[1] := 1: for j from 2 to 150 do for m from 1 to j-1 do if j mod m = 0 then a[j] := a[j]+a[m] fi: od: od: for k from 1 to 150 do printf(`%d, `, a[k]) od: # from James A. Sellers Dec 07 2000

(PARI) A002033(n) = if(n==1, 1, sumdiv(n, i, if(i==n, 0, A002033(i)))) [From Michael Porter (michael_b_porter(AT)yahoo.com), Nov 01 2009]

Apart from initial term, same as A074206. Cf. A001055, A050324. a(A002110)=A000670.

Cf. A000123, A100529, A117621.

Sequence in context: A079616 A097283 A118314 this_sequence A074206 A108466 A087145

Adjacent sequences: A002030 A002031 A002032 this_sequence A002034 A002035 A002036

nonn,core,easy,nice

N. J. A. Sloane (njas(AT)research.att.com).