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A208260 Nonprime numbers starting and ending with digit 1. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Complement of A062332 with respect to A208259. Supersequence of A208261 (nonprime numbers with all divisors starting and ending with digit 1).
LINKS
FORMULA
(1 - A010051(a(n))) * A000030(a(n)) * (a(n) mod 10) = 1. - Reinhard Zumkeller, Jul 16 2014
MATHEMATICA
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 *)
PROG
(Haskell)
a208260 n = a208260_list !! (n-1)
a208260_list = filter ((== 0) . a010051') a208259_list
-- Reinhard Zumkeller, Jul 16 2014
CROSSREFS
Cf. A208259 (number starting and ending with a number 1), A062332 (primes starting and ending with a number 1).
Sequence in context: A326109 A338111 A351060 * A222724 A343760 A280635
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Feb 24 2012
STATUS
approved

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Last modified March 28 04:13 EDT 2024. Contains 371235 sequences. (Running on oeis4.)