OFFSET
1,2
COMMENTS
For the notion of m-multiset repetition class defining partitions of n see a comment in A185976 (with N replaced by n), and the characteristic array A176723 of such partitions in Abramowitz-Stegun order.
Note that there may be more than one multiset repetition class defining partition of n with minimal number of parts a(n). E.g., n=12, a(12)= 6, with two such partitions 1^2,2^2,3^2 and 1^3,2,3,4.
FORMULA
a(n)= min(sum(e[j],j=1..M)) with sum(j*e[j],j=1..M)=n, e[1]>=e[2]>=...>=e[M]>=1, and largest part M.
M takes all values from 1,...,Mmax(n), where Mmax(n) is the index of the largest triangular number from A000217 smaller or equal to n. E.g., Mmax(7) = 3.
EXAMPLE
The multiset repetition class defining partitions with minimal number of parts a(n) are, for n=1,...,12:
1^1; 1^2; 1,2; 1^2,2; 1^3,2; 1,2,3; 1^2,2,3; 1^3,2,3;
1^2,2^2,3; 1,2,3,4; 1^2,2,3,4;
1^3,2,3,4, 1^2,2^2,3^2;...
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Mar 07 2011
EXTENSIONS
Changed by the author in response to comments from Franklin T. Adams-Watters, Apr 02 2011.
STATUS
approved