A250290 Numbers k such that Euler(k) (A122045(k)) is a semiprime.

8, 10, 14, 26, 30, 58, 78

Offset

1,1

Comments

No more terms <= 200.

k=7634 is a term, but it is not known to be the next term after 78. - Jeppe Stig Nielsen, May 12 2023

Links

Table of n, a(n) for n=1..7.

Hisanori Mishima, Euler numbers (n = 0 to 78).

Hisanori Mishima, Euler numbers (n = 80 to 106).

Prime Pages, -E(7634)/1559.

Sam Wagstaff, Factorization of Bernoulli and Euler numbers.

Example

a(2) = 10 so Euler(10) = 50521 = 19 * 2659 is a semiprime.

Prog

(PARI) is(k) = k%2==0 && bigomega(eulerfrac(k))==2 \\ slow, from Jeppe Stig Nielsen, May 12 2023

Crossrefs

Cf. A103234, A122045.

Sequence in context: A326386 A027693 A196226 * A228946 A100718 A063190

Adjacent sequences: A250287 A250288 A250289 * A250291 A250292 A250293

Keyword

nonn,more

Author

Eric Chen, Dec 24 2014

Status

approved