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A106127 Numbers k such that k-th semiprime == 2 (mod k). 0
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 (list; graph; refs; listen; history; text; internal format)
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.

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.

Sequence in context: A009626 A009835 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

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Last modified September 17 12:26 EDT 2021. Contains 347477 sequences. (Running on oeis4.)