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Integer_partitions Calculator

Integer_partitions

Function: integer_partitions (<n>)

num_partitions (5) = cardinality (integer_partitions (5));
 num_partitions (8, list);
 num_partitions (n);

Function: integer_partitions (<n>, <len>) Returns integer partitions of <n>, that is, lists of integers which sum to <n>.

integer_partitions(<n>) returns the set of all partitions of the integer <n>. Each partition is a list sorted from greatest to least.

integer_partitions(<n>, <len>) returns all partitions that have length <len> or less; in this case, zeros are appended to each partition with fewer than <len> terms to make each partition have exactly <len> terms. Each partition is a list sorted from greatest to least.

A list [a_1, ..., a_m] is a partition of a nonnegative integer n when (1) each a_i is a nonzero integer, and (2) a_1 + ... + a_m = n. Thus 0 has no partitions.

Examples:

          (%i1) integer_partitions (3);
          (%o1)               {[1, 1, 1], [2, 1], [3]}
          (%i2) s: integer_partitions (25)$
          (%i3) cardinality (s);
          (%o3)                         1958
          (%i4) map (lambda ([x], apply ("+", x)), s);
          (%o4)                         {25}
          (%i5) integer_partitions (5, 3);
          (%o5) {[2, 2, 1], [3, 1, 1], [3, 2, 0], [4, 1, 0], [5, 0, 0]}
          (%i6) integer_partitions (5, 2);
          (%o6)               {[3, 2], [4, 1], [5, 0]}

To find all partitions that satisfy a condition, use the function subset; here is an example that finds all partitions of 10 that consist of prime numbers.

          (%i1) s: integer_partitions (10)$
          (%i2) cardinality (s);
          (%o2)                          42
          (%i3) xprimep(x) := integerp(x) and (x > 1) and primep(x)$
          (%i4) subset (s, lambda ([x], every (xprimep, x)));
          (%o4) {[2, 2, 2, 2, 2], [3, 3, 2, 2], [5, 3, 2], [5, 5], [7, 3]}

(%o1)                                true
(%i2) 

Integer_partitions Example

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