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A077379
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Smallest n-digit squarefree number whose internal as well as external digits form a squarefree number greater than 1; or 0 if no such number exists.
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4
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0, 0, 123, 1021, 10021, 100021, 1000021, 10000021, 100000021, 1000000021, 10000000021, 100000000021, 1000000000021, 10000000000021, 100000000000021
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Note that the pattern is broken for any n == 3 (mod 22), where 10^(n-1)+21 is divisible by 11^2. - Frank Adams-Watters (FrankTAW(AT)Netscape.net), Jun 13 2006
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EXAMPLE
| a(5) = 10021 = 11 * 911 is squarefree, internal digits 002 squarefree, external digits 11 squarefree.
a(6) = 100021 = 29 * 3449 has exactly those same properties.
a(7) = 1000021 = 11 * 90911 has exactly those same properties.
a(8) = 10000021 = 97 * 103093 has exactly those same properties.
a(9) = 100000021 = 11 * 19 * 23 * 71 * 293 is similar, though not semiprime.
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CROSSREFS
| Cf. A077376, A077377, A077378, A077380.
Cf. A077376, A077377, A077378, A077380.
Sequence in context: A181679 A193251 A074303 * A135475 A116935 A174173
Adjacent sequences: A077376 A077377 A077378 * A077380 A077381 A077382
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KEYWORD
| base,more,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 06 2002
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EXTENSIONS
| a(5)-a(12) from Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 22 2006
More terms from Frank Adams-Watters (FrankTAW(AT)Netscape.net), Jun 13 2006
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