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A356770
a(n) is the number of equations in the set {x+2y=n, 2x+3y=n, ..., k*x+(k+1)*y=n, ..., n*x+(n+1)*y=n} which admit at least one nonnegative integer solution.
2
1, 2, 3, 4, 4, 5, 5, 6, 6, 7, 6, 8, 7, 8, 8, 9, 8, 10, 8, 10, 10, 10, 9, 12, 10, 11, 11, 12, 10, 13, 11, 13, 12, 12, 12, 15, 12, 13, 13, 15, 12, 15, 13, 15, 15, 14, 13, 17, 14, 16, 15, 16, 14, 17, 15, 17, 16, 16, 15, 20, 15, 16, 17, 18, 17, 19, 16, 18, 17, 19, 16, 21, 17, 18, 19, 19
OFFSET
1,2
COMMENTS
a(n) = ceiling(2*(sqrt(n)-1)) + ceiling(A000005(n)/2).
EXAMPLE
a(5) = 4. Consider the equations: x+2y=5, 2x+3y=5, 3x+4y=5, 4x+5y=5, 5x+6y=5. Only four of them admit at least one nonnegative integer solution, since 3x+4y=5 has no nonnegative integer solution.
MATHEMATICA
b[m_] := m;
f[n_] := Table[Dimensions[Solve[b[k]*x + b[k + 1]*y == n, {x, y}, NonNegativeIntegers]][[1]], {k, 1, n}];
Flatten[Table[Dimensions[DeleteCases[f[k], 0]], {k, 1, 100}]]
CROSSREFS
Cf. A000005.
Sequence in context: A196162 A071940 A085883 * A265912 A094192 A093874
KEYWORD
nonn
AUTHOR
Luca Onnis, Aug 27 2022
STATUS
approved