Exercise · ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-008 · ★★☆ Intermediate
Expand \(x(x+1)(x+2)=\sum_k c(3,k)\,x^k\). What is \(c(3,2)\)?
Choose one option.
Show answer
- D. 3
Explanation
Expanding gives \(x^3+3x^2+2x\), and the coefficient of \(x^2\) is 3.
Review the concept: Stirling number of the first kind
The Stirling number of the first kind \(c(n,k)\) counts the permutations of \(n\) elements that have exactly \(k\) cycles.
\[x(x+1)\cdots(x+n-1)=\sum_{k=0}^{n} c(n,k)\,x^{k}\]
More practice problems: stirling number of the first kind
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-001 What does the number c(n,k) count?
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-002 The permutations of \1,2,3\ with a single cycle are the 3-cycles. What is c(3,1)?
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-003 What is c(n,n) for every n≥ 1?
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-004 What is c(n,0) for n≥ 1?
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-005 What is c(n,1)?
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-006 Use c(4,1)=6, c(4,2)=11, c(4,3)=6 and c(4,4)=1. What is the sum of the row n=4?
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-007 With c(4,2)=11 and c(4,1)=6, use c(n,k)=(n-1)c(n-1,k)+c(n-1,k-1) to find c(5,2).
- ZW-STIRLING-NUMBER-OF-THE-FIRST-KIND-009 Using the row n=4, where c(4,1)=6, c(4,2)=11, c(4,3)=6 and c(4,4)=1, compute ∑_k=1^4 k c(4,k).
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