[R] how to get a numeric vector?

[vod vos]

Hi,

a <- c(1, 4)
b <- c(5, 8)

a:b

[1] 1 2 3 4 5
Warning messages:
1: In a:b : numerical expression has 2 elements: only the first used
2: In a:b : numerical expression has 2 elements: only the first used

how to get:

c(1:5, 4:8)

Thanks.