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 A208261 Nonprime numbers with all divisors starting and ending with digit 1. 4
 1, 121, 1111, 1331, 1441, 1661, 1991, 10201, 11231, 11341, 11561, 11671, 12001, 12221, 12661, 12881, 12991, 13211, 13231, 13541, 14201, 14311, 14531, 14641, 14971, 15191, 15251, 15851, 15961, 16181, 16291, 16621, 16841, 17161, 17281, 17611, 17831, 18271, 18281 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Complement of A062332 with respect to A208262. Subsequence of A208260 (nonprime numbers starting and ending with digit 1). LINKS Harvey P. Dale, Table of n, a(n) for n = 1..3000 EXAMPLE Divisors of 1111: 1, 11, 101, 1111. MATHEMATICA Select[Table[n, {n, 20000}], ! PrimeQ[#] && Union[First /@ IntegerDigits[Divisors[#]]] == {1} && Union[Last /@ IntegerDigits[Divisors[#]]] == {1} &] (* Vladimir Joseph Stephan Orlovsky, Feb 26 2012 *) d1Q[n_]:=Module[{idn=IntegerDigits[n]}, First[idn]==Last[idn]==1]; Select[ Range[1, 20000, 10], !PrimeQ[#]&&Count[Divisors[#], _?d1Q] == DivisorSigma[ 0, #]&] (* Harvey P. Dale, Nov 23 2012 *) CROSSREFS Cf. A208262 (numbers with all divisors starting and ending with digit 1), A062332 (primes starting and ending with digit 1). Sequence in context: A175983 A307858 A329100 * A036928 A088171 A254970 Adjacent sequences:  A208258 A208259 A208260 * A208262 A208263 A208264 KEYWORD nonn,base AUTHOR Jaroslav Krizek, Feb 24 2012 STATUS approved

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Last modified May 23 16:11 EDT 2022. Contains 353976 sequences. (Running on oeis4.)