Output the n-th Bell Number
JavaScript (ES6), 47 bytes

f=(n,a=[b=1])=&gt;n--?f(n,[b,...a.map(e=&gt;b+=e)]):b
f=(n,a=[b=1])=&gt;--n?f(n,[b,...a.map(e=&gt;b+=e)]):b


First one is 0-indexed, second is 1-indexed.