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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

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

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