#Haskell, fortyfour 30 28 bytes

(>>=tail.show.(+4).fromEnum)

Using the +4 approach from Adnan's answer saves 14 bytes.

Try it on Ideone. Usage:

> (>>=tail.show.(+4).fromEnum)"codegolf"
"0315040507151206"

Two bytes off thanks to xnor. Old version:

f a=['0'|a<'k']++(show$fromEnum a-96)
(f=<<)

Haskell, fortyfour 30 28 bytes

(>>=tail.show.(+4).fromEnum)

Using the +4 approach from Adnan's answer saves 14 bytes.

Try it on Ideone. Usage:

> (>>=tail.show.(+4).fromEnum)"codegolf"
"0315040507151206"

Two bytes off thanks to xnor. Old version:

f a=['0'|a<'k']++(show$fromEnum a-96)
(f=<<)

#Haskell, fortyfour 30 28 bytes

(>>=tail.show.(+4).fromEnum)

Using the +4 approach from Adnan's answer saves 14 bytes.

Try it on Ideone. Usage:

> (>>=tail.show.(+4).fromEnum)"codegolf"
"0315040507151206"

Two bytes off thanks to xnor. Old version:

f a=['0'|a<'k']++(show$fromEnum a-96)
(f=<<)

#Haskell, fortyfour 30 28 bytes

(>>=tail.show.(+4).fromEnum)

Using the +4 approach from Adnan's answer saves 14 bytes.

Try it on Ideone. Usage:

> (>>=tail.show.(+4).fromEnum)"codegolf"
"0315040507151206"

Two bytes off thanks to xnor. Old version:

f a=['0'|a<'k']++(show$fromEnum a-96)
(f=<<)

#Haskell, fortyfour 30 bytes

(>>=(tail.show.(+4).fromEnum))

Using the +4 approach from Adnan's answer saves 14 bytes.

Try it on Ideone. Usage:

> (>>=(tail.show.(+4).fromEnum))"codegolf"
"0315040507151206"

Old version:

f a=['0'|a<'k']++(show$fromEnum a-96)
(f=<<)

#Haskell, fortyfour 30 28 bytes

(>>=tail.show.(+4).fromEnum)

Using the +4 approach from Adnan's answer saves 14 bytes.

Try it on Ideone. Usage:

> (>>=tail.show.(+4).fromEnum)"codegolf"
"0315040507151206"

Two bytes off thanks to xnor. Old version:

f a=['0'|a<'k']++(show$fromEnum a-96)
(f=<<)