A235690 Semiprimes which have one or more occurrences of exactly two different digits.

10, 14, 15, 21, 25, 26, 34, 35, 38, 39, 46, 49, 51, 57, 58, 62, 65, 69, 74, 82, 85, 86, 87, 91, 93, 94, 95, 115, 118, 119, 121, 122, 133, 141, 155, 161, 166, 177, 202, 221, 226, 262, 299, 303, 323, 334, 335, 339, 355, 377, 393, 411, 422, 445, 446, 447, 454

Offset

1,1

Comments

The first term having a repeated digit is 115.

Links

Table of n, a(n) for n=1..57.

Example

1000000000010101 is a term because it is made of the digits 0 and 1 and it is the product of the two primes 18463559 and 54160739.

Mathematica

Select[Range[454], Length@Union@ IntegerDigits[#] == 2 && Total[Last /@ FactorInteger[#]] == 2 &] (* Giovanni Resta, Jan 14 2014 *)

Prog

(PARI)
list(lim)=my(v=List(), t); forprime(p=2, sqrt(lim), t=p; forprime(q=p, lim\t, listput(v, t*q))); vecsort(Vec(v)) \\ From A001358
b=list(10000); s=[]; for(n=1, #b, if(#vecsort(eval(Vec(Str(b[n]))), , 8)==2, s=concat(s, b[n]))); s

Crossrefs

Cf. A235691-A235696.

Cf. A235154-A235161.

Sequence in context: A087247 A307507 A171156 * A271568 A229271 A088711

Adjacent sequences: A235687 A235688 A235689 * A235691 A235692 A235693

Keyword

nonn,base

Author

Colin Barker, Jan 14 2014

Status

approved