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.
%I A107073 #18 Jul 31 2025 22:03:06
%S A107073 3,9,11,17,27,29,33,39,41,47,57,59,71,81,83,93,107,111,117,129,141,
%T A107073 149,153,159,171,201,221,227,251,257,267,279,281,291,311,317,323,327,
%U A107073 339,353,363,381,393,401,407,419,423,437,447,449,461,491,507,509,521,527
%N A107073 Numbers k such that the string 35k is prime.
%e A107073 If k=47 then 3547 is prime.
%p A107073 A055642 := proc(n) max(1,ilog10(n)+1) ; end: cat2 := proc(a,b) a*10^A055642(b)+b ; end: for n from 1 to 1000 do if isprime( cat2(35,n) ) then printf("%d,",n) ; fi; od: # _R. J. Mathar_, Jan 16 2009
%t A107073 Select[Range[600],PrimeQ[FromDigits[Join[{3,5},IntegerDigits[#]]]]&] (* _Harvey P. Dale_, Jun 06 2015 *)
%o A107073 (Magma) [ n: n in [1..900] | IsPrime(Seqint(Intseq(n) cat [5, 3])) ]; // _Vincenzo Librandi_, Feb 03 2011
%Y A107073 Cf. A032666. - _R. J. Mathar_, Jan 16 2009
%K A107073 nonn,base
%O A107073 1,1
%A A107073 _Parthasarathy Nambi_, Jun 07 2005