A309102 Nonnegative integers that are not the sum of two refactorable numbers.

0, 1, 5, 6, 7, 8, 12, 15, 22, 23, 28, 29, 31, 34, 35, 39, 40, 43, 46, 47, 50, 51, 53, 55, 56, 59, 63, 66, 67, 70, 71, 75, 77, 79, 83, 87, 91, 94, 95, 99, 101, 103, 107, 111, 115, 118, 119, 121, 123, 125, 127, 131, 135, 139, 142, 143, 147, 149, 151, 155, 159

Offset

1,3

Links

Table of n, a(n) for n=1..61.

Eric Weisstein's World of Mathematics, Refactorable Number

Mathematica

Flatten[Table[If[Sum[(1 - Ceiling[i/DivisorSigma[0, i]] + Floor[i/DivisorSigma[0, i]]) (1 - Ceiling[(n - i)/DivisorSigma[0, n - i]] + Floor[(n - i)/DivisorSigma[0, n - i]]), {i, Floor[n/2]}] == 0, n, {}], {n, 0, 200}]]

Prog

(PARI) isok(n) = n%numdiv(n) == 0;
is(n) = sum(j=1, n-1, isok(j)&&isok(n-j)) == 0; \\ Jinyuan Wang, Jul 27 2019

Crossrefs

Cf. A033950, A309346.

Sequence in context: A178502 A047322 A236242 * A080703 A284682 A171405

Adjacent sequences: A309099 A309100 A309101 * A309103 A309104 A309105

Keyword

nonn

Author

Wesley Ivan Hurt, Jul 27 2019

Status

approved