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

1,1

Comments

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

Links

Table of n, a(n) for n=1..40.

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

Prog

(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(Nmax<t=(k+j5)^3-k^3, break); a=concat(a, t))); vecsort(a) } \\ M. F. Hasler, Jun 07 2007

Crossrefs

Intersection of A017329 and A181123.

Sequence in context: A191943 A046011 A038853 * A120536 A043391 A063358

Adjacent sequences: A038857 A038858 A038859 * A038861 A038862 A038863

Keyword

nonn,base

Author

Jeff Burch

Extensions

Corrected by M. F. Hasler, Jun 07 2007

Status

approved