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

1,3

Links

Table of n, a(n) for n=1..18.

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

Crossrefs

Cf. A077376, A077377, A077378, A077379.

Sequence in context: A264130 A282405 A077362 * A063052 A231708 A172158

Adjacent sequences: A077377 A077378 A077379 * A077381 A077382 A077383

Keyword

base,nonn

Author

Amarnath Murthy, Nov 06 2002

Extensions

More terms from R. J. Mathar, Sep 26 2006

Status

approved