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A208260
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Nonprime numbers starting and ending with digit 1.
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3
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1, 111, 121, 141, 161, 171, 1001, 1011, 1041, 1071, 1081, 1101, 1111, 1121, 1131, 1141, 1161, 1191, 1211, 1221, 1241, 1251, 1261, 1271, 1281, 1311, 1331, 1341, 1351, 1371, 1391, 1401, 1411, 1421, 1431, 1441, 1461, 1491, 1501, 1521, 1541, 1551, 1561, 1581, 1591
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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Complement of A062332 with respect to A208259. Supersequence of A208261 (nonprime numbers with all divisors starting and ending with digit 1).
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LINKS
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Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
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FORMULA
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(1 - A010051(a(n))) * A000030(a(n)) * (a(n) mod 10) = 1. - Reinhard Zumkeller, Jul 16 2014
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MATHEMATICA
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Select[Range[2000], ! PrimeQ[#] && First[IntegerDigits[#]] == 1 && Last[IntegerDigits[#]] == 1 &] (* Vladimir Joseph Stephan Orlovsky, Feb 26 2012 *)
Join[{1}, Select[Range[2000], CompositeQ[#]&&NumberDigit[#, 0] == NumberDigit[ #, IntegerLength[ #]-1]==1&]] (* Harvey P. Dale, Aug 01 2021 *)
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PROG
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(Haskell)
a208260 n = a208260_list !! (n-1)
a208260_list = filter ((== 0) . a010051') a208259_list
-- Reinhard Zumkeller, Jul 16 2014
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CROSSREFS
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Cf. A208259 (number starting and ending with a number 1), A062332 (primes starting and ending with a number 1).
Cf. A010051, A017281, A131835, A000030.
Sequence in context: A326109 A338111 A351060 * A222724 A343760 A280635
Adjacent sequences: A208257 A208258 A208259 * A208261 A208262 A208263
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KEYWORD
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nonn,base
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AUTHOR
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Jaroslav Krizek, Feb 24 2012
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STATUS
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approved
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