A202276 Number of integers k <= n such that sigma(x) = k has no solution, sigma = A000203.

0, 1, 1, 1, 2, 2, 2, 2, 3, 4, 5, 5, 5, 5, 5, 6, 7, 7, 8, 8, 9, 10, 11, 11, 12, 13, 14, 14, 15, 15, 15, 15, 16, 17, 18, 18, 19, 19, 19, 19, 20, 20, 21, 21, 22, 23, 24, 24, 25, 26, 27, 28, 29, 29, 30, 30, 30, 31, 32, 32, 33, 33, 33, 34, 35, 36, 37, 37, 38, 39

Offset: 1

Author

Jaroslav Krizek, Dec 25 2011

Keywords

• nonn

Comments

Partial sums of A175253.

Examples

			a(9) = 3 because sigma(x) = k has no solution for k = 2, 5 and 9.
		

Links

• Jaroslav Krizek, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A074753, A202277, A202275, A175523, A007369, A007368, A007609.

Programs

Mathematica

seq[max_] := Module[{t = Table[0, {max}]}, t[[Complement[Range[max], Table[ DivisorSigma[1, n], {n, 1, max}]]]] = 1; Accumulate@ t]; seq[100] (* Amiram Eldar, Dec 20 2024 *)