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 A235687 #14 Mar 18 2023 12:12:07 %S A235687 46,49,62,65,69,91,93,94,95,106,141,142,143,145,146,155,158,159,213, %T A235687 214,215,217,218,219,221,226,253,254,259,262,265,267,334,335,339,341, %U A235687 346,355,358,381,382,386,391,393,394,395,398,466,469,493,497,511,514 %N A235687 Semiprimes which remain semiprimes when the rightmost digit is removed. %H A235687 Harvey P. Dale, <a href="/A235687/b235687.txt">Table of n, a(n) for n = 1..1000</a> %e A235687 514 is in the sequence because 51 = 3*17. %t A235687 Select[Range[600],PrimeOmega[#]==2==PrimeOmega[FromDigits[ Most[ IntegerDigits[ #]]]]&] (* _Harvey P. Dale_, Oct 02 2014 *) %t A235687 Select[Range[600],PrimeOmega[#]==PrimeOmega[Quotient[#,10]]==2&] (* _Harvey P. Dale_, Mar 18 2023 *) %o A235687 (PARI) %o A235687 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 A235687 issemiprime(n) = n>0 && bigomega(n)==2 %o A235687 t=list(1000); for(n=1, #t, if(issemiprime(t[n]\10), print1(t[n],", "))) %Y A235687 Cf. A235688, A235689. %Y A235687 Cf. A227919, A227916, A069686. %K A235687 nonn,base %O A235687 1,1 %A A235687 _Colin Barker_, Jan 14 2014