A067237 Numbers k such that gcd(sigma(k),k) = k/5.

5, 10, 15, 30, 60, 90, 140, 420, 1170, 2480, 3360, 6200, 7440, 8190, 18600, 40640, 114660, 121920, 131040, 297600, 997920, 2618880, 5059200, 64995840, 72602880, 95472000, 102136320, 167751680, 197308800, 433305600, 503255040, 668304000, 714954240, 1307124000, 1381161600, 1502582400

Offset

1,1

Comments

Also numbers k such that denominator(sigma(k)/k) = 5. - David A. Corneth, Oct 15 2023

Links

David A. Corneth, Table of n, a(n) for n = 1..166 (first 61 terms from Jud McCranie, terms <= 10^28)

Example

30 is in the sequence as gcd(sigma(30), 30) = gcd(72, 30) = 6 = 30/5. - David A. Corneth, Oct 15 2023

Prog

(PARI) is(n) = gcd(sigma(n), n) == n/5 - David A. Corneth, Oct 15 2023

Crossrefs

Cf. A000203.

Cf. similar sequences with A017666(n)=k: A159907 (k=2), A245775 (k=3), A229088 (k=4), A262359 (k=6).

Sequence in context: A138521 A225701 A022600 * A196157 A048703 A020332

Adjacent sequences: A067234 A067235 A067236 * A067238 A067239 A067240

Keyword

nonn

Author

Benoit Cloitre, Feb 20 2002

Extensions

More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 15 2004

Status

approved