A072604 Last digit of n, phi(n) and sigma(n) is 0 in base 10.

440, 600, 950, 1000, 1240, 1320, 1350, 1400, 1450, 1640, 1900, 2090, 2200, 2440, 2600, 2700, 2840, 2850, 2900, 2950, 2970, 3000, 3080, 3190, 3400, 3720, 3800, 3950, 3960, 4040, 4180, 4200, 4350, 4450, 4600, 4750, 4840, 4920, 5240, 5400, 5450, 5700

Offset

1,1

Comments

This sequence is infinite. 440 * k is in the sequence for odd k > 0 and k, 440 are coprime. - David A. Corneth, Apr 01 2018

Links

David A. Corneth, Table of n, a(n) for n = 1..16811 (all terms up to 10^6)

Formula

Does lim n -> infinity a(n)/n exist?

Example

phi(1240)=480, sigma(1240)=2880, hence 1240 is in the sequence.

Mathematica

Select[Range[6000], Mod[{#, EulerPhi[#], DivisorSigma[1, #]}, 10]=={0, 0, 0}&] (* Harvey P. Dale, Apr 01 2018 *)

Prog

(PARI) isok(n) = !(n % 10) && !(eulerphi(n) % 10) && ! (sigma(n) % 10); \\ Michel Marcus, Nov 26 2013

Crossrefs

Cf. A000010, A000203.

Subsequence of A072589.

Sequence in context: A345809 A279812 A279950 * A158319 A250879 A247722

Adjacent sequences: A072601 A072602 A072603 * A072605 A072606 A072607

Keyword

base,nonn

Author

Benoit Cloitre, Aug 06 2002

Status

approved