A052425 Numbers with no two-digit factors (apart from itself).

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25, 27, 29, 31, 35, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 202

Offset

1,2

Links

David A. Corneth, Table of n, a(n) for n = 1..10000

Example

From David A. Corneth, Aug 20 2020: (Start)
202 is in the sequence as the divisors of 202 are 1, 2, 101, 202 and none have two digits (in base 10).
20 isn't in the sequence as 20 is divisible by 10 which has two digits in base 10 and isn't 20. (End)

Mathematica

ntdfQ[n_]:=Union[IntegerLength[#]==2&/@Most[Divisors[n]]]=={False}; Join[ {1}, Select[Range[250], ntdfQ]] (* Harvey P. Dale, Sep 26 2021 *)

Prog

(PARI) is(n) = for(i = 10, min(n-1, 99), if(n % i == 0, return(0))); 1 \\ David A. Corneth, Aug 20 2020

Crossrefs

Sequence in context: A326880 A359077 A078453 * A272074 A246097 A275776

Adjacent sequences: A052422 A052423 A052424 * A052426 A052427 A052428

Keyword

base,nonn

Author

Henry Bottomley, Mar 14 2000

Status

approved