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

1,1

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

Cf. A106582, A019549, A030459.

Sequence in context: A196581 A179245 A174651 * A039445 A300144 A247528

Adjacent sequences: A225133 A225134 A225135 * A225137 A225138 A225139

Keyword

nonn,base,less

Author

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

Status

approved