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A077380
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Largest n-digit squarefree number whose internal as well as external digits form a squarefree number, or 0 if no such number exists.
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5
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0, 0, 977, 9977, 99987, 999987, 9999987, 99999977, 999999985, 9999999987, 99999999987, 999999999987, 9999999999987, 99999999999987, 999999999999987, 9999999999999987, 99999999999999987, 999999999999999987
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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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 (mathar(AT)strw.leidenuniv.nl), Sep 26 2006
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CROSSREFS
| Cf. A077376, A077377, A077378, A077379.
Sequence in context: A205252 A190400 A077362 * A063052 A172158 A108904
Adjacent sequences: A077377 A077378 A077379 * A077381 A077382 A077383
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 06 2002
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 26 2006
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