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 A077380 #8 Aug 07 2015 02:42:14
%S A077380 0,0,977,9977,99987,999987,9999987,99999977,999999985,9999999987,
%T A077380 99999999987,999999999987,9999999999987,99999999999987,
%U A077380 999999999999987,9999999999999987,99999999999999987,999999999999999987
%N A077380 Largest n-digit squarefree number whose internal as well as external digits form a squarefree number, or 0 if no such number exists.
%p A077380 with(numtheory) ; A077380 := proc(n) local anmax,leadd,edit,idit ; anmax := 10^n-1 ; while anmax >= 10^(n-1) do leadd := floor(anmax/10^(n-1)) ; edit := 10*leadd + ( anmax mod 10 ); idit := floor(anmax/10) -leadd*10^(n-2) ; if issqrfree(anmax) and issqrfree(edit) and issqrfree(idit) then RETURN(anmax) ; fi ; anmax := anmax-1 ; od ; RETURN(0) ; end: printf("0,") ; for n from 2 to 30 do printf("%d,",A077380(n)) ; od ; # _R. J. Mathar_, Sep 26 2006
%Y A077380 Cf. A077376, A077377, A077378, A077379.
%K A077380 base,nonn
%O A077380 1,3
%A A077380 _Amarnath Murthy_, Nov 06 2002
%E A077380 More terms from _R. J. Mathar_, Sep 26 2006