find the nth pentagonal number in typescript

index.ts
function getPentagonalNumber(n: number): number {
  return n * (3 * n - 1) / 2;
}

// Example usage
const nth = 6;
const pentagonalNumber = getPentagonalNumber(nth);
console.log(`The ${nth}th pentagonal number is ${pentagonalNumber}`);
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index.ts
The 6th pentagonal number is 35
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