# Tribonacci sequence

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**A** simplistic puzzle from The Riddler when applying brute force:

A Tribonacci sequence is based on three entry integers a ≤ b ≤ c, and subsequent terms are the sum of the previous three. Among Tribonacci sequences containing 2023, which one achieves the smallest fourth term, a+b+c ?

The R code

tri<-function(a,b,e){ while(F<2023){ F=a+b+e;a=b;b=e;e=F} return(F<2024)} sol=NULL;m=674 for(a in 1:m) for(b in a:m) for(e in b:m) if(tri(a,b,e)){ sol=rbind(sol,c(a,b,e))}

leads to (1,1,6) as the solution… Incidentally, this short exercise led me to finally look for a fix to entering vectors as arguments of functions requesting lists:

do.call("tri",as.list(sol[2023,]))

To

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