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Find 7 Digit Prime palindrome in Pi
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| pi <- read.csv("./pi.csv", header=FALSE, sep=" ") | |
| dig <- 14000 | |
| pistr <- paste(c(pi[1,]$V2, ".", head(pi[-1,], dig-1)$V2), collapse="") | |
| is.palindrome <- function (word) { identical(word, paste(rev(strsplit(word, "")[[1]]), collapse="")) } | |
| is.prime <- function(n) n == 2L || all(n %% 2L:floor(sqrt(n)) != 0) | |
| base <- 1 | |
| end <- 7 | |
| repeat { | |
| if (is.palindrome(substr(pistr, base, end)) & is.prime(as.numeric(substr(pistr, base, end)))) { | |
| print(substr(pistr, base, end)) | |
| break | |
| } | |
| base <- base + 1 | |
| end <- end + 1 | |
| } |
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| http://oeis.org/A000796/b000796.txt |
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nathanjohnson320@vm-2:~$ time Rscript pi.R
[1] "9149419"
real 0m3.155s
user 0m3.055s
sys 0m0.075s