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 A215477 #20 Nov 15 2023 01:14:04 %S A215477 4,6,9,34,123,789,901,1234,34567,56789,901234,1234567,7890123, %T A215477 567890123,12345678901,345678901234567,4567890123456789, %U A215477 12345678901234567,890123456789012345,3456789012345678901,456789012345678901234,123456789012345678901234567,1234567890123456789012345678901,23456789012345678901234567890123 %N A215477 Semiprimes with consecutive (ascending) digits. %C A215477 This is to semiprimes A001358 as A006055 is to primes. %e A215477 a(9) = 34567 because it is semiprime 13 * 2659, and (3,4,5,6,7) are consecutive ascending digits. %p A215477 R:= 4, 6, 9: V:= [$1..9]: %p A215477 for d from 2 to 50 do %p A215477 V:= map(n -> 10*n + ((n+1) mod 10), V); %p A215477 W:= select(t -> numtheory:-bigomega(t)=2, V); %p A215477 R:= R, op(W); %p A215477 od: %p A215477 R; # _Robert Israel_, Nov 15 2023 %Y A215477 Cf. A001358, A118697, A059043, A006055, A161760. %K A215477 nonn,base %O A215477 1,1 %A A215477 _Jonathan Vos Post_, Aug 12 2012 %E A215477 Corrected and extended by _R. J. Mathar_, Aug 13 2012