Repeated Indexing / Sequence Operation

Hi Everyone,

quick question before the end of the year.

I have soem indices to select data from a bigger sample. I want to select n
days before each index and n days after the index. Any clever way to do it.
A for loop would do but I wanted to know if there is a moreR-friendly way to
approach this

Example
# InitialIndices
i2 = (90, 190, 290)

# Indices I want to end up with
i3 = c(85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 185, 186, 187, 188, 189,
190, 191, 192, 193, 194, 195
285, 286, 287, 288, 289, 290, 291, 292, 293, 294, 295)
# A way to get Final Indices
SampleWidth
i3 = c(i2)
for (j in seq(1, SampleWidth )) {
i3 = c(i3, i2 + j )
?i3 = c(i3, i2 - j )
?}