Things have been going wild since I opened this blog. Tasks were piled up while I was tight on time. At present, I’m facing a major challenge in my life. However, I decide to spare some time for self-improvements.
R is one of the most useful tool I’ve learned in my research life. Learning R has been always in my to-do list but my practice is not enough. Thus, I’m starting a learning program, in which to solve problems in Project Euler would help me with R coding and mathematics thinking as well.
OK, enough talking. Let’s have a look at the very first problem of Euler’s.

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num <- seq(1, 999)
multiples.3 <- num[num %% 3 == 0]
multiples.5 <- num[num %% 5 == 0]
num.request <- union(multiples.3, multiples.5)
result <- sum(num.request)
cat("The sum of all the multiples of 3 or 5 below 1000 is ", result, ".\n", 
    sep="")

I read the posts in Project Euler Forum, and two thoughts should be mentioned.

1. The sum of multiples of any given number a is easy to calculate with a*int(n/a)*(int(n/a)+1)/2.
2. Firstly find those not multiples of 3 or 5, then subtract them from the sum of all.