A122732 3-almost primes that are the sum of 2 positive cubes. Sums of 2 positive cubes, with the sums having exactly 3 prime divisors counted with multiplicity.

28, 370, 539, 637, 730, 854, 1001, 1358, 1547, 1729, 2198, 2261, 3059, 3887, 3925, 4075, 4123, 4706, 4825, 4921, 5038, 5957, 6293, 6886, 6923, 7075, 7163, 7202, 7657, 8029, 8729, 9262, 9269, 9325, 9331, 10745, 10955, 11458, 12175, 12383, 12845

Offset: 1

Author

Jonathan Vos Post, Sep 23 2006

Keywords

• easy
• nonn

Comments

3-almost prime analog of A085366 Semiprimes that are the sum of two positive cubes. The sum of two positive cubes cannot be prime.

Examples

			a(1) = 28 = 2^2 * 7 = 1^3 + 3^3.
a(2) = 370 = 2 * 5 * 37 = 3^3 + 7^3.
a(3) = 539 = 7^2 * 11 = 2^3 + 8^3.
a(4) = 637 = 7^2 * 13 = 5^3 + 8^3.
a(5) = 730 = 2 * 5 * 73 = 1^3 + 9^3.
a(6) = 854 = 2 * 7 * 61 = 5^3 + 9^3.
a(7) = 1001 = 7 * 11 * 13 = 1^3 + 10^3.
		

Links

• Giovanni Resta, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000578, A001222, A003325, A014612.

Programs

PARI

is(n)=bigomega(n)==3 && #select(v->min(v[1], v[2])>0, thue('x^3+1, n))>0 \\ Charles R Greathouse IV, Feb 05 2017

Formula

A003325 INTERSECTION A014612. {x = a^3 + b^3 for positive integers a, b, such that A001222(x) = 3}.

Extensions

More terms from R. J. Mathar, Jan 27 2009