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

1,2

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 A357169

Adjacent sequences: A208258 A208259 A208260 * A208262 A208263 A208264

Keyword

nonn,base

Author

Jaroslav Krizek, Feb 24 2012

Status

approved