A077380 Largest n-digit squarefree number whose internal as well as external digits form a squarefree number, or 0 if no such number exists.
0, 0, 977, 9977, 99987, 999987, 9999987, 99999977, 999999985, 9999999987, 99999999987, 999999999987, 9999999999987, 99999999999987, 999999999999987, 9999999999999987, 99999999999999987, 999999999999999987
Offset: 1
Programs
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Maple
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
Extensions
More terms from R. J. Mathar, Sep 26 2006