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 A235688 #15 Jun 07 2017 09:33:29 %S A235688 14,26,34,39,46,49,69,74,86,94,106,115,121,122,133,134,146,155,158, %T A235688 169,177,185,187,194,206,209,214,215,221,226,235,249,262,265,274,287, %U A235688 291,295,309,314,321,326,334,335,339,346,355,358,362,365,377,382,386,391 %N A235688 Semiprimes which remain semiprimes when the leftmost digit is removed. %H A235688 Harvey P. Dale, <a href="/A235688/b235688.txt">Table of n, a(n) for n = 1..1000</a> %e A235688 249 is in the sequence because 49 = 7*7. %t A235688 Select[Range[400],PrimeOmega[#]==PrimeOmega[Mod[#,10^(IntegerLength[ #]-1)]] == 2&] (* _Harvey P. Dale_, Jun 07 2017 *) %o A235688 (PARI) %o A235688 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 A235688 delleft(a) = my(b, c); b=#Str(a); c=a\(10^(b-1)); a-c*(10^(b-1)) %o A235688 issemiprime(n) = n>0 && bigomega(n)==2 %o A235688 t=list(500); for(n=1, #t, if(issemiprime(delleft(t[n])), print1(t[n],", "))) %Y A235688 Cf. A235687, A235689. %Y A235688 Cf. A227919, A227916, A069686. %K A235688 nonn,base %O A235688 1,1 %A A235688 _Colin Barker_, Jan 14 2014