A038860 Numbers ending with '5' that are the difference of two positive cubes.

215, 335, 485, 665, 875, 1115, 1385, 1685, 2015, 2375, 2765, 3185, 3635, 4095, 4115, 4625, 4905, 5165, 5735, 5805, 6335, 6795, 6965, 7625, 7875, 8315, 9035, 9045, 9785, 10305, 10565, 11375, 11655, 12215, 13085, 13095, 13985, 14625, 14915, 15875

Offset: 1

Author

Jeff Burch

Keywords

• nonn
• base

Comments

Contains (k+5(2j+1))^3-k^3 for any integers k,j>=0. - M. F. Hasler, May 31 2007

Crossrefs

Intersection of A017329 and A181123.

Programs

PARI

A038860(Nmax=20000,a=[]) = { local(t, j5); forstep( j=1,Nmax^(1/3)/5,2, j5=5*j; for(k=1, sqrt((Nmax/j5-j5^2-3*j5)/3), if(NmaxM. F. Hasler, Jun 07 2007

Formula

A number is in this sequence iff it is of the form (k+10j-5)^3-k^3, where k,j are any positive integers, since (k+d)^3 - k^3 = d(3(k+d/2)^2+d^2/4) == 5 (mod 10) iff d is odd and d == 0 (mod 5) (cf. A038853) - M. F. Hasler, Jun 07 2007

Extensions

Corrected by M. F. Hasler, Jun 07 2007