The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 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). Cf. A010051, A017281, A131835, A000030. Sequence in context: A326109 A338111 A351060 * A222724 A343760 A280635 Adjacent sequences:  A208257 A208258 A208259 * A208261 A208262 A208263 KEYWORD nonn,base AUTHOR Jaroslav Krizek, Feb 24 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 29 20:36 EDT 2022. Contains 354913 sequences. (Running on oeis4.)