A206288 Nonprime numbers with all divisors starting with digit 1.

1, 121, 143, 169, 187, 1111, 1133, 1177, 1199, 1243, 1313, 1331, 1339, 1391, 1397, 1417, 1441, 1469, 1507, 1529, 1573, 1639, 1651, 1661, 1703, 1717, 1727, 1751, 1781, 1793, 1807, 1819, 1837, 1853, 1859, 1903, 1919, 1921, 1937, 1957, 1963, 1969, 1991

Offset

1,2

Comments

Subsequence of A206286, A131835.

Complement of A045707 (primes with first digit 1) with respect to A202287 (numbers with all divisors starting with digit 1).

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

All divisors of 1859 (1, 11, 13, 169, 1859) start with digit 1.

Maple

fd1:= n -> n < 2*10^ilog10(n):
filter:= proc(n) not isprime(n) and andmap(fd1, numtheory:-divisors(n)) end proc:
select(filter, [1, seq(seq(i, i=10^d+1..2*10^d-1, 2), d=1..3)]); # Robert Israel, Mar 13 2019

Mathematica

fQ[n_] := Module[{d = Divisors[n]}, Union[IntegerDigits[#][[1]] & /@ d] == {1}]; Select[Range[1991], ! PrimeQ[#] && fQ[#] &] (* T. D. Noe, Feb 13 2012 *)

Crossrefs

Cf. A045707 (primes with first digit 1), A202287 (numbers with all divisors starting with digit 1).

Sequence in context: A038511 A285784 A062649 * A287390 A258202 A242372

Adjacent sequences: A206285 A206286 A206287 * A206289 A206290 A206291

Keyword

nonn,base

Author

Jaroslav Krizek, Feb 12 2012

Status

approved