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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
OFFSET
1,2
COMMENTS
Complement of A062332 with respect to A208262. Subsequence of A208260 (nonprime numbers starting and ending with digit 1).
LINKS
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 A357169
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Feb 24 2012
STATUS
approved