A131850 Odious 3-almost primes.

8, 28, 42, 44, 50, 52, 70, 76, 98, 110, 117, 124, 138, 148, 164, 171, 174, 182, 186, 188, 230, 236, 242, 244, 261, 266, 268, 273, 279, 285, 286, 290, 292, 310, 316, 322, 333, 345, 357, 369, 370, 385, 388, 406, 410, 412, 425, 426, 428, 434, 436, 465, 475, 477

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

A014612 INTERSECTION A000069.

Example

a(1) = 8 because 8 = 2^3 is divisible by exactly 3 primes (counted with multiplicity) and 8 (base 2) = 1000 has an odd number (1) of ones in its binary expansion.
a(2) = 28 = 2^2 * 7 = 11100 (base 2) has an odd number (1) of ones in its binary expansion.

Maple

isA014612 := proc(n) if numtheory[bigomega](n) = 3 then true ; else false ; fi ; end: isA000069 := proc(n) bdigs := convert(n, base, 2) ; if add(i, i=bdigs) mod 2 = 1 then true; else false ; fi ; end: isA131850 := proc(n) isA000069(n) and isA014612(n) ; end: for n from 1 to 500 do if isA131850(n) then printf("%d, ", n) fi ; od: # R. J. Mathar, Oct 24 2007

Mathematica

Select[Range[500], PrimeOmega[#]==3&&OddQ[DigitCount[#, 2, 1]]&] (* Harvey P. Dale, Jun 11 2017 *)

Prog

(PARI) list(lim)=my(v=List(), t); forprime(p=2, lim\4, forprime(q=2, min(lim\(2*p), p), t=p*q; forprime(r=2, min(lim\t, q), if(hammingweight(t*r)%2, listput(v, t*r))))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Mar 29 2013

Crossrefs

Cf. A000069, A014612.

Sequence in context: A121739 A166729 A202290 * A009504 A001486 A230211

Adjacent sequences: A131847 A131848 A131849 * A131851 A131852 A131853

Keyword

easy,nonn,less

Author

Jonathan Vos Post, Oct 04 2007

Extensions

More terms from R. J. Mathar, Oct 24 2007

Status

approved