A387462 Composite cyclic numbers that are of the form 4n-1.

15, 35, 51, 87, 91, 95, 115, 119, 123, 143, 159, 187, 215, 235, 247, 255, 259, 267, 287, 295, 299, 303, 319, 323, 335, 339, 371, 391, 395, 403, 407, 411, 415, 427, 435, 447, 451, 455, 511, 515, 519, 527, 535, 551, 559, 583, 591, 595, 611, 623, 635, 667, 671, 679

Offset

1,1

Links

Table of n, a(n) for n=1..54.

Example

As 15 = 3*5, 15 is composite; as gcd(15,phi(15)) = gcd(15,8) = 1, it is cyclic (an element of A050384), and as 15 = 4*4 - 1, it is congruent to 3 mod 4 or of the forms 4*n-1 or 4*n+3.

Maple

q:= n-> not isprime(n) and igcd(n, numtheory[phi](n))=1:
select(q, [4*i+3$i=1..170])[];  # Alois P. Heinz, Sep 04 2025

Mathematica

Select[Range[3, 1000, 4], CompositeQ[#] && CoprimeQ[#, EulerPhi[#]] &] (* Amiram Eldar, Aug 29 2025 *)

Crossrefs

Intersection of A050384 and A004767.

Cf. A387460, A003277, A091236.

Sequence in context: A201018 A187400 A162280 * A290781 A340449 A063532

Adjacent sequences: A387459 A387460 A387461 * A387463 A387464 A387465

Keyword

nonn

Author

Joel E. Cohen, Aug 29 2025

Status

approved