A225136 Numbers that are concatenations of triprimes.

88, 128, 188, 208, 278, 288, 308, 428, 448, 458, 508, 528, 638, 668, 688, 708, 758, 768, 788, 808, 812, 818, 820, 827, 828, 830, 842, 844, 845, 850, 852, 863, 866, 868, 870, 875, 876, 878, 888, 892, 898, 899, 928, 988, 998, 1028, 1058, 1108, 1148, 1168, 1178

Offset: 1

Author

Kevin L. Schwartz and Christian N. K. Anderson, Apr 29 2013

Keywords

• nonn
• base
• less

Examples

			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.
		

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.

Crossrefs

Cf. A106582, A019549, A030459.

Programs

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)