#Groovy, 26 bytes

This answer was basically stolen from @Geobits.

a={n->n--?a(n)*~-a(n)+1:2} 

Took that answer and, using groovy shortcuts, optimized it further.

Groovy, 26 bytes

This answer was basically stolen from @Geobits.

a={n->n--?a(n)*~-a(n)+1:2} 

Took that answer and, using groovy shortcuts, optimized it further.

#Groovy, 26 bytes

This answer was basically stolen from @Geobits.

a={n->n--?a(n)*~-a(n)+1:2} 

Took that answer and, using groovy shortcuts, optimized it further.

#Groovy, 26 bytes

This answer was basically stolen from @Geobits.

a={n->n--?a(n)*~-a(n)+1:2} 

Took that answer and, using groovy shortcuts, optimized it further.