A098271 Nonprime numbers n such that phi(n) divides n^2 - 1, where phi(n) (A000010) is Euler's totient function.

1, 15, 35, 65, 91, 255, 377, 559, 1295, 2001, 2059, 2431, 4081, 7743, 8911, 10745, 12851, 22791, 26335, 39689, 51271, 61699, 65535, 73151, 95201, 97681, 112897, 114191, 139231, 150177, 184255, 216545, 229503, 286937, 294785, 296191, 334369

Offset

1,2

Comments

Number of terms < 10^k: 1, 5, 8, 15, 26, 46, 71, 105, 160, 228, ..., . Robert G. Wilson v, Jan 10 2018

Links

Robert G. Wilson v, Table of n, a(n) for n = 1..229 (first 99 terms from G. C. Greubel)

Mathematica

Select[ Range[ 335000], Mod[ #^2 - 1, EulerPhi[ # ]] == 0 && !PrimeQ[ # ] &]

Prog

(PARI) isok(n) = !isprime(n) && !((n^2-1) % eulerphi(n)); \\ Michel Marcus, Jan 11 2018

Crossrefs

Cf. A000010, A097605.

Sequence in context: A146656 A229108 A160497 * A234542 A242235 A082663

Adjacent sequences: A098268 A098269 A098270 * A098272 A098273 A098274

Keyword

nonn

Author

Leroy Quet and Robert G. Wilson v, Sep 01 2004

Status

approved