OFFSET
1,1
EXAMPLE
10258 is in the sequence because 10258 = 2*23*223 and 223 is the concatenation of 2 with 23.
MATHEMATICA
c[x_, y_] := x 10^IntegerLength[y] + y; upto[mx_] := Sort@ Reap[Block[{p=2, q=3, v=1}, While[v <= mx, While[p < q && (v = p q (r = c[p, q])) <= mx, If[PrimeQ@r, Sow@v]; p = NextPrime[p]]; p=2; q = NextPrime[q]; v = p q c[p, q]]]][[2, 1]]; upto[10^6] (* Giovanni Resta, Apr 14 2017 *)
PROG
(PARI) isok(n) = f = factor(n); ((#f~ == 3) && (vecmax(f[, 2]) == 1) && (f[3, 1] == fromdigits(concat(digits(f[1, 1]), digits(f[2, 1]))))); \\ Michel Marcus, Apr 14 2017
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Peter Weiss, Apr 14 2017
STATUS
approved