A106127 Numbers k such that k-th semiprime == 2 (mod k).

1, 2, 4, 39, 51, 52, 71, 6920, 613377, 613381, 613405, 613433, 613437, 613449, 613455, 613536, 613537, 613548, 613557, 613569, 613581, 613583, 613587, 613588, 613608, 613613, 58155550, 58155570, 6384425447, 6384425465, 6384425505, 6384425531, 6384425567

Offset

1,2

Comments

No more terms through 160788536. - Ryan Propper, May 09 2006

a(34) > 10^12. - Lucas A. Brown, Oct 17 2020

Links

Table of n, a(n) for n=1..33.

Lucas A. Brown, semiprimemods.py

Example

a(3)=4 is a term because the 4th semiprime (i.e., 10) == 2 (mod 4).

Mathematica

SemiprimeQ[n_] := (Plus @@ Last /@ FactorInteger[n] == 2); i = 0; Do[If[SemiprimeQ[n], i++; If[Mod[n, i] == 2, Print[i]]], {n, 10^9}] (* Ryan Propper, May 09 2006 *)

Crossrefs

Cf. A001358, A356755.

Sequence in context: A009835 A362411 A009834 * A018992 A098625 A057777

Adjacent sequences: A106124 A106125 A106126 * A106128 A106129 A106130

Keyword

hard,nonn

Author

Shyam Sunder Gupta, May 07 2005

Extensions

More terms from Ryan Propper, May 09 2006

a(1), a(2), and a(29)-a(33) from Lucas A. Brown, Oct 17 2020

Status

approved