A242677 Semiprimes whose binary representation, read in decimal, is also semiprime.

15, 33, 55, 57, 65, 69, 77, 87, 115, 121, 129, 143, 169, 205, 209, 265, 299, 305, 321, 339, 361, 415, 417, 447, 451, 481, 493, 505, 517, 519, 535, 551, 553, 581, 611, 623, 667, 687, 695, 721, 737, 779, 789, 799, 865, 871, 893, 901, 905, 923, 943, 949, 955, 973

Offset

1,1

Links

K. D. Bajpai, Table of n, a(n) for n = 1..10000

Example

a(2) = 33 = 3 * 11 is semiprime. Binary representation of 33 = 100001 = 11 * 9091 which is also semiprime.
a(4) = 57 = 3 * 19 is semiprime. Binary representation of 57 = 111001 = 11 * 10091 which is also semiprime.

Maple

with(numtheory):A242677 := proc() if bigomega(n)=2 and bigomega(convert(n, binary))=2 then RETURN (n) ; fi; end:  seq(A242677(), n=1..2000);

Mathematica

c = 0; Do[If [PrimeOmega[n] == 2 && PrimeOmega[FromDigits[IntegerDigits[n, 2]]] == 2, c ++;  Print[c, "  ", n]], {n, 1, 3*10^5}];

Crossrefs

Cf. A001358, A236365, A236537, A241764.

Sequence in context: A357934 A327900 A071965 * A020184 A231371 A228318

Adjacent sequences: A242674 A242675 A242676 * A242678 A242679 A242680

Keyword

nonn,base

Author

K. D. Bajpai, May 20 2014

Status

approved