A111496 4-almost primes with semiprime digits (digits 4, 6, 9 only).

444, 644, 664, 666, 966, 996, 999, 4444, 4466, 4494, 4696, 4964, 6644, 6666, 6699, 9444, 9496, 9646, 9964, 9966, 9999, 44444, 44499, 44646, 44996, 46444, 46449, 46964, 46996, 49444, 49494, 49946, 49966, 49996, 64446, 64494, 64644, 64666

Offset: 1

Author

Jonathan Vos Post, Nov 16 2005

Keywords

• base
• easy
• nonn

Examples

			a(1) = 444 = 2^2 * 3 * 37, a(2) = 644 = 2^2 * 7 * 23, a(3) = 664 = 2^3 * 83, a(4) = 666 = 2 * 3^2 * 37, a(5) = 966 = 2 * 3 * 7 * 23, a(6) = 996 = 2^2 * 3 * 83, a(7) = 999 = 3^3 * 37, a(8) = 4466 = 2 * 7 * 11 * 29, a(9) = 4494 = 2 * 3 * 7 * 107, a(10) = 4696 = 2^3 * 587.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358, A014613, A107665, A107666, A107342, A111494, A111697.

Programs

PARI

do(N)=my(v=List(), a=[4, 6, 9]); for(d=1, N, forvec(u=vector(d, i, [1, 3]), t=fromdigits(apply(n->a[n], u)); if(bigomega(t)==4, listput(v, t)))); Set(v) \\ Charles R Greathouse IV, Feb 01 2017