library(igraph)
g <- sample_smallworld(1, 100, 5, 0.1)

> get.shortest.paths(g,4,19)
$vpath
$vpath[[1]]
+ 4/100 vertices, from f2866bd:
[1]   4 100  98  19

d1 <- unlist(neighborhood(g, 1, 4, mode="out"))
[1] 20 28 96 97 36 59 44 60 98 10 31 11 24 12 34 47 13 19 14 58 62 88 94 95

d1 <- unlist(neighborhood(g, 1, 4, mode="out"))
 d2 <- unlist(neighborhood(g, 2, 4, mode="out"))
 d3 <- setdiff(d2,d1)
[1] 20 28 96 97 36 59 44 60 98 10 31 11 24 12 34 47 13 19 14 58 62 88 94 95

> unlist(neighborhood(g, 1, 19, mode="out"))
 [1] 19  8 14 15 16 17 18 20 21 22 24 66 92 98