>> f 1 2 3 4 5 6 7
<< 2 3 5 7

_4 	The largest prime smaller than y
_1 	π(y), the number of primes less than y (same as p:^:_1)
0 	1 if y is not prime
1 	1 if y is prime
2 	a 2-row table of the prime factors and exponents in the factorization of y (same as __ q: y)
3 	the list of primes whose product is equal to y (same as q: y)
4 	The smallest prime larger than y
5 	The number of integers less than or equal to y that are relatively prime to y (Euler's totient function φ(y))

Leaderboard (evaluated):
Jelly:       !¡
05AB1E:      F!                (swaps order)
Actually:    `!`n
MATL:        :":p
CJam:        q~{m!}*
Pyth:        u.!GEQ
Pyth:        Mem=.!GH
Jolf:        e+*j"!Y                (swaps order)
Mathematica: #!&~Nest~##&
J:           4 :'(!^:y)x'
J:           4 :0\n(!^:y)x\n)
J:           ".@($&'!'@[,":@])
UGL:         iilRc%l$d:_l*%:%rd:_o
Haskell:     f 0 y=y\nf x y=product[1..f(x-1)y]                (swaps order)
Ruby:        ->a,b{eval'a=(1..a).inject:*;'*b}