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A373971
a(n) = 1 if n can be represented as a sum of 2 distinct positive cubes, otherwise 0.
5
0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1
OFFSET
0
COMMENTS
Differs from A025468 first at n=1729, where a(1729) = 1, while A025468(1729) = 2.
FORMULA
a(n) = signum(A025468(n)) = [A025468(n) > 0], where [ ] is the Iverson bracket.
a(n) <= A373972(n).
a(n) <= A373973(n).
EXAMPLE
a(9) = 1 as 9 = 2^3 + 1^3.
a(35) = 1 as 35 = 3^3 + 2^3.
PROG
(PARI) A373971(n) = if(0==n, n, for(i=ceil(sqrtn(n\2+1, 3)), sqrtn(n-(1/2), 3), if(ispower(n-(i^3), 3), return(1))); 0); \\ After M. F. Hasler's Apr 12 2008 program in A024670.
CROSSREFS
Characteristic function of A024670.
Cf. A010057, A025468, A373972, A373973, A373974 (inverse Möbius transform).
Sequence in context: A297039 A239705 A025468 * A025465 A323514 A369660
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jun 24 2024
STATUS
approved