login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A235690 Semiprimes which have one or more occurrences of exactly two different digits. 8
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 27 09:09 EST 2020. Contains 331293 sequences. (Running on oeis4.)