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 A235689 #16 Nov 22 2018 11:20:36 %S A235689 141,142,143,145,146,161,166,169,194,247,249,262,265,267,291,295,298, %T A235689 299,341,346,361,362,365,391,393,394,395,398,445,446,447,466,469,493, %U A235689 497,542,543,545,562,565,566,591,597,649,662,667,669,694,695,697,698,699 %N A235689 Semiprimes which remain semiprimes when the leftmost and rightmost digits are removed. %e A235689 169 = 13^2 is in the sequence because 6 = 2*3. %t A235689 Select[Range[100,700],PrimeOmega[#]==PrimeOmega[FromDigits[ Rest[ Most[ IntegerDigits[ #]]]]] ==2&] (* _Harvey P. Dale_, Nov 22 2018 *) %o A235689 (PARI) %o A235689 list(lim)=my(v=List(), t); forprime(p=2, sqrt(lim), t=p; forprime(q=p, lim\t, listput(v, t*q))); vecsort(Vec(v)) \\ From A001358 %o A235689 delleft(a) = my(b, c); b=#Str(a); c=a\(10^(b-1)); a-c*(10^(b-1)) %o A235689 issemiprime(n) = n>0 && bigomega(n)==2 %o A235689 t=list(700); for(n=1, #t, if(issemiprime(delleft(t[n]\10)), print1(t[n],", "))) %Y A235689 Cf. A235687, A235688. %Y A235689 Cf. A227919, A227916, A069686. %K A235689 nonn,base %O A235689 1,1 %A A235689 _Colin Barker_, Jan 14 2014