(solved it) FRIENDS PAIRING PROBLEM, didn't get the recurrence relation

[hetp111 (Het Patel)]

Friends Pairing Problem - GeeksforGeeks

https://hack.codingblocks.com/contests/c/141/1092

not getting the recurrence relation…
f(n)=f(n-1)+(n-1) * f(n-2)

[Anubhav-Aron-1353657628083250 (Anubhav Aron)]

Solved on WhatsApp Group…