OFFSET
1,1
LINKS
Christian N. K. Anderson, Table of n, a(n) for n = 1..10000
Christian N. K. Anderson, Table of n, a(n), all possible separations of a(n) into triprimes for n=1..10000.
EXAMPLE
88 = 8|8, both of which are triprime because 8=2*2*2.
458 = 45 | 8 = 3*3*5 | 2*2*2.
12428 can be split into triprimes in three ways: 12|428, 12|42|8, and 124|28.
PROG
(R) library(gmp); istriprime=function(x) ifelse(x<8, F, length(factorize(x))==3)
splithasproperty<-function(n, FUN, curdig=1, res=list(), curspl=c()) {
no0<-function(s){ while(substr(s, 1, 1)=="0" & nchar(s)>1) s=substr(s, 2, nchar(s)); s}
s=as.character(n)
if(curdig>nchar(s)) return(res)
if(length(curspl)>0) if(FUN(as.bigz(no0(substr(s, curdig, nchar(s)))))) res[[length(res)+1]]=curspl
for(i in curdig:nchar(s))
if(FUN(as.bigz(no0(substr(s, curdig, i)))))
res=splithasproperty(n, FUN, i+1, res, c(curspl, i))
res
}
which(sapply(1:500, function(x) length(splithasproperty(x, istriprime)))>0)
CROSSREFS
KEYWORD
nonn,base,less
AUTHOR
Kevin L. Schwartz and Christian N. K. Anderson, Apr 29 2013
STATUS
approved