This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a={1, 3, 7, 9};
Flatten[Table[Mod[Abs[10-Prime[n]], 10]*10+a, {n, 50}]]
10141 is a term as a concatenation of prime(26)=101 followed by prime(13)=41.
a:=proc(k) local s,m: s:= [op(convert(ithprime(k),base,10)),op(convert(ithprime(2*k),base,10))]: m:=add(s[j]*10^(j-1),j=1..nops(s)): if not isprime(m) then RETURN(NULL) else RETURN(m) fi: end; seq(a(k),k=1..250); (C. Ronaldo)
Select[Table[FromDigits[Flatten[IntegerDigits/@{Prime[2n],Prime[n]}]],{n,250}],PrimeQ] (* Harvey P. Dale, Nov 17 2014 *)
c[r_, s_] := ToExpression[ToString[r] <> ToString[s]]; Do[k = 1; While[ !PrimeQ[c[Prime[n*k], Prime[k]]], k++ ]; Print[c[Prime[n*k], Prime[k]]], {n, 2, 100}] (* Ryan Propper, Sep 14 2005 *)