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

1,1

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.

Links

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

Formula

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

Example

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.

Prog

(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

Crossrefs

Cf. A000578, A001222, A003325, A014612.

Sequence in context: A138452 A276286 A125440 * A010944 A022623 A077507

Adjacent sequences: A122729 A122730 A122731 * A122733 A122734 A122735

Keyword

easy,nonn

Author

Jonathan Vos Post, Sep 23 2006

Extensions

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

Status

approved