A369254 Numbers k that have an odd number of divisors that are at most sqrt(k).

1, 2, 3, 5, 7, 11, 12, 13, 16, 17, 18, 19, 20, 23, 28, 29, 31, 32, 36, 37, 41, 43, 44, 45, 47, 48, 50, 52, 53, 59, 61, 63, 67, 68, 71, 73, 75, 76, 79, 80, 81, 83, 89, 92, 97, 98, 99, 100, 101, 103, 107, 109, 112, 113, 116, 117, 124, 127, 131, 137, 139, 147, 148, 149, 151, 153, 157, 162, 163, 164, 167, 171, 172, 173

Offset

1,2

Links

Table of n, a(n) for n=1..74.

Example

1 has just one divisor 1, which is <= sqrt(1), therefore 1 is included.
Of the two divisors of 2, [1, 2], only 1 is at most sqrt(2), therefore 2 is included.
Of the three divisors of 4, [1, 2, 4], the first two are <= sqrt(4), and as two is not an odd number, 4 is NOT included in this sequence.

Prog

(PARI) \\ See A369253.

Crossrefs

Positions of odd terms in A038548.

Cf. A369253 (characteristic function).

Sequence in context: A230918 A001742 A307714 * A073085 A340657 A316793

Adjacent sequences: A369251 A369252 A369253 * A369255 A369256 A369257

Keyword

nonn

Author

Antti Karttunen, Jan 24 2024

Status

approved