A373973 a(n) = 1 if n can be expressed as (a^3 + b^3)/(a*b) with b > a >= 1, otherwise 0.

0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1

Offset

1

Comments

a(n) = 1 if n has a divisor that is a sum of 2 distinct positive cubes (i.e., is one of the terms of A024670), otherwise 0.

Links

Antti Karttunen, Table of n, a(n) for n = 1..100080

Index entries for characteristic functions

Formula

a(n) = signum(A373974(n)) = [A373974(n) > 0], where [ ] is the Iverson bracket.

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.
A373973(n) = { fordiv(n, d, if(A373971(d), return(1))); 0; };

Crossrefs

Characteristic function of A359225.

Cf. A024670, A373971, A373974.

Sequence in context: A353569 A353477 A044939 * A371084 A353626 A347244

Adjacent sequences: A373970 A373971 A373972 * A373974 A373975 A373976

Keyword

nonn

Author

Antti Karttunen, Jun 24 2024

Status

approved