A265711 Numbers n such that floor(Sum_{d|n} 1 / sigma(d)) = 1.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73

Offset

1,2

Comments

Numbers n such that A265710(n) = floor(A265708(n) / A069934(n)) = floor(A265709(n) / A265710(n)) = 1.

See A265714(n) = the smallest number k such that floor(Sum_{d|k} 1/sigma(d)) = n.

Links

G. C. Greubel, Table of n, a(n) for n = 1..9268

Example

6 is a term because floor(Sum_{d|6} 1/sigma(d)) = floor(1/1 + 1/3 + 1/4 + 1/12) = floor(5/3) = 1.

Mathematica

Select[Range@ 73, Floor[Sum[1/DivisorSigma[1, d], {d, Divisors@ #}]] == 1 &] (* Michael De Vlieger, Dec 31 2015 *)

Prog

(Magma) [n: n in [1..1000] | Floor(&+[1/SumOfDivisors(d): d in Divisors(n)]) eq 1]
(PARI) isok(n) = floor(sumdiv(n, d, 1/sigma(d))) == 1; \\ Michel Marcus, Dec 27 2015

Crossrefs

Cf. A069934, A000203, A265708, A265709, A265710, A265712, A265713, A265714, A266227, A266228.

Sequence in context: A272159 A227981 A085736 * A262065 A296765 A055643

Adjacent sequences: A265708 A265709 A265710 * A265712 A265713 A265714

Keyword

nonn

Author

Jaroslav Krizek, Dec 25 2015

Status

approved