A280862 Numbers n such that A258409(n) * A002322(n) = A000010(n), where A258409(1) = 1.

1, 2, 4, 6, 10, 14, 15, 18, 21, 22, 26, 33, 34, 35, 38, 39, 45, 46, 50, 51, 54, 55, 57, 58, 62, 65, 69, 74, 75, 77, 82, 85, 86, 87, 91, 93, 94, 95, 98, 99, 106, 111, 115, 118, 119, 122, 123, 129, 133, 134, 135, 141, 142, 143, 145, 146, 147, 153, 155, 158, 159, 161, 162, 166, 175, 177

Offset: 1

Author

Thomas Ordowski and Altug Alkan, Jan 09 2017

Keywords

• nonn

Comments

Squarefree terms > 2 give A006881.

Even terms are even terms of A033948.

No terms of the form p^k > 4, where p is a prime.

The sequence has natural density 0. - Information from Carl Pomerance, Jan 09 2017

Links

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

Crossrefs

Cf. A000010, A002322, A006881, A033948, A258409.

Programs

Mathematica

{1}~Join~Select[Range@ 180, (GCD @@ (Divisors[#] - 1)) CarmichaelLambda@ # == EulerPhi@ # &] (* Michael De Vlieger, Jan 10 2017 *)

PARI

a258409(n) = if(n%2==0, return(1)); if(n%3==0, return(2)); if(n%5==0 && n%4 != 1, return(2)); gcd(apply(p->p-1, factor(n)[, 1]));
a002322(n) = lcm(znstar(n)[2]);
is(n) = a258409(n) * a002322(n) == eulerphi(n);