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A333821
Numbers k that can be represented in the form k = p^3 - q^3 - r^3, where p, q, r are positive integers satisfying p = q + r.
0
6, 18, 36, 48, 60, 90, 126, 144, 162, 168, 210, 216, 252, 270, 288, 330, 360, 378, 384, 396, 468, 480, 486, 540, 546, 594, 630, 720, 750, 792, 816, 858, 918, 924, 972, 990, 1008, 1026, 1140, 1152, 1170, 1260, 1296, 1344, 1386, 1404, 1518, 1530, 1560, 1620, 1638, 1656, 1680, 1728, 1800
OFFSET
1,1
COMMENTS
An alternative representation of k is k = 3*q*r*(q+r), with q, r positive integers, then k is a multiple of 6.
FORMULA
a(n) = 6 * A121741(n).
EXAMPLE
60 is in the sequence because 60 = 5^3 - 4^3 - 1^3, with 5 = 4 + 1.
PROG
(PARI) ok(n) = {my(i=1, a=0, m=0, j); if(n%6==0, while(a<=n&&m==0, j=1; while(j<i&&m==0, a=3*i*j*(i-j); if(a==n, m=1); j+=1); i+=1)); m}
CROSSREFS
KEYWORD
nonn
AUTHOR
Antonio Roldán, Apr 06 2020
STATUS
approved