A208261 Nonprime numbers with all divisors starting and ending with digit 1.

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

Author

Jaroslav Krizek, Feb 24 2012

Keywords

• nonn
• base

Comments

Complement of A062332 with respect to A208262. Subsequence of A208260 (nonprime numbers starting and ending with digit 1).

Examples

			Divisors of 1111: 1, 11, 101, 1111.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..3000

Crossrefs

Cf. A208262 (numbers with all divisors starting and ending with digit 1), A062332 (primes starting and ending with digit 1).

Programs

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 *)