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In mathematics, an empty sum, or nullary sum, [1] is a summation where the number of terms is zero. The natural way to extend non-empty sums [ 2 ] is to let the empty sum be the additive identity . Let a 1 {\displaystyle a_{1}} , a 2 {\displaystyle a_{2}} , a 3 {\displaystyle a_{3}} , ... be a sequence of numbers, and let
For example, summation of [1, 2, 4, 2] is denoted 1 + 2 + 4 + 2, and results in 9, that is, 1 + 2 + 4 + 2 = 9. Because addition is associative and commutative, there is no need for parentheses, and the result is the same irrespective of the order of the summands. Summation of a sequence of only one summand results in the summand itself.
Computation of the sum 2 + 5 + 8 + 11 + 14. When the sequence is reversed and added to itself term by term, the resulting sequence has a single repeated value in it, equal to the sum of the first and last numbers (2 + 14 = 16). Thus 16 × 5 = 80 is twice the sum.
Negative numbers do not have any compositions, but 0 has one composition, the empty sequence. Each positive integer n has 2 n−1 distinct compositions. Bijection between 3 bit binary numbers and compositions of 4. A weak composition of an integer n is similar to a composition of n, but allowing terms of the sequence to be zero: it is a way of ...
t(n) = C(n + 1, 2) = n(n + 1) / 2 = 1 + 2 + ... + n for n ≥ 1, with t(0) = 0 (empty sum). A000217: Square numbers n 2: 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, ... n 2 = n × n: A000290: Tetrahedral numbers T(n) 0, 1, 4, 10, 20, 35, 56, 84, 120, 165, ... T(n) is the sum of the first n triangular numbers, with T(0) = 0 (empty sum). A000292 ...
If f has a unique left identity e, the definition of F l can be modified to operate on empty sequences by defining the value of F l on an empty sequence to be e (the previous base case on sequences of length 1 becomes redundant). Similarly, F r can be modified to operate on empty sequences if f has a unique right identity.
This sequence of arithmetic means converges to 1 ⁄ 2, so the Cesàro sum of Σa k is 1 ⁄ 2. Equivalently, one says that the Cesàro limit of the sequence 1, 0, 1, 0, … is 1 ⁄ 2. [2] The Cesàro sum of 1 + 0 − 1 + 1 + 0 − 1 + · · · is 2 ⁄ 3. So the Cesàro sum of a series can be altered by inserting infinitely many 0s as well as ...
The following is a matrix-based approach to generating primitive triples with generalized Fibonacci sequences. [9] Start with a 2 × 2 array and insert two coprime positive integers (q,q′) in the top row. Place the even integer (if any) in the left-hand column.