A129293 Numbers m such that m^4-1 has no divisors d with 1 < d < m-1.

3, 4, 6, 150, 180, 240, 270, 420, 570, 1290, 1320, 2310, 2550, 2730, 3360, 3390, 4260, 4650, 5850, 5880, 6360, 6780, 9000, 9240, 9630, 10530, 10890, 11970, 13680, 13830, 14010, 14550, 16230, 16650, 18060, 18120, 18540, 19140, 19380, 21600, 21840, 23370

Offset: 1

Author

Reinhard Zumkeller, Apr 09 2007

Keywords

• nonn

Comments

Essentially the same as A070155, since m^4-1=(m-1)(m+1)(1+m^2). - R. J. Mathar, Jun 14 2008

Examples

			{1,5,7,35,37,185,259,1295} is the set of divisors of 6^4-1, therefore 6 is a term, A129292(6) = #{1,3} = 2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A070155, A129292, A129295, A129297.

Programs

PARI

is(k) = k == 3 || (isprime(k-1) && isprime(k+1) && isprime(k^2+1)); \\ Amiram Eldar, Apr 15 2024

Formula

A129292(a(n)) = #{1, a(n)-1} = 2.