A235691 - OEIS

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A235691

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

106, 123, 129, 134, 142, 143, 145, 146, 158, 159, 169, 178, 183, 185, 187, 194, 201, 203, 205, 206, 209, 213, 214, 215, 217, 218, 219, 235, 237, 247, 249, 253, 254, 259, 265, 267, 274, 278, 287, 289, 291, 295, 298, 301, 302, 305, 309, 314, 319, 321, 326, 327

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

The first term having a repeated digit is 1003.

LINKS

Table of n, a(n) for n=1..52.

EXAMPLE

91119111691966691969 is a term, because it is made of the 3 digits {1, 6, 9} and is the product of two primes 9397848521 and 9695741689. - Giovanni Resta, Jan 14 2014

MATHEMATICA

Select[Range@999, Length@ Union@ IntegerDigits[#] == 3 && 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)==3, s=concat(s, b[n]))); s

CROSSREFS

Cf. A235690, A235692-A235696.

Cf. A235154-A235161.

Sequence in context: A277605 A102804 A192994 * A095645 A039554 A186458

Adjacent sequences: A235688 A235689 A235690 * A235692 A235693 A235694

KEYWORD

nonn,base

AUTHOR

Colin Barker, Jan 14 2014

STATUS

approved