A160725 Cyclops semiprimes.

106, 201, 202, 203, 205, 206, 209, 301, 302, 303, 305, 309, 403, 407, 501, 502, 505, 703, 706, 707, 802, 803, 807, 901, 905, 11013, 11014, 11015, 11017, 11019, 11021, 11023, 11029, 11031, 11035, 11038, 11041, 11042, 11051, 11053

Offset

1,1

Comments

Cyclops numbers (A134808) that are also semiprimes (A001358).

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

g:= proc(x, n)
  local L, i;
  L:= convert(x+9^(2*n), base, 9);
  add((L[i]+1)*10^(i-1), i=1..n)+add((L[i]+1)*10^i, i=n+1..2*n)
end proc:
select(t -> numtheory:-bigomega(t)=2, [seq(seq(g(i, n), i=0..9^(2*n)-1), n=1..2)]); # Robert Israel, Jan 20 2019

Mathematica

Select[Range@ 12000, And[OddQ@ #2, #3[[Ceiling[#2/2] ]] == 0, Count[#3, 0] == 1, PrimeOmega@ #1 == 2] & @@ {#, IntegerLength@ #, IntegerDigits@ #} &] (* or *)
Select[Flatten@ Table[a (10^(d + 1)) + b, {d, 2}, {a, FromDigits /@ Tuples[Range@ 9, {d}]}, {b, FromDigits /@ Tuples[Range@ 9, {d}]}], PrimeOmega@ # == 2 &] (* Michael De Vlieger, Jan 20 2019 *)

Crossrefs

Cf. A001358, A134808, A134809, A138131, A138148, A153806, A153807, A160711, A160712, A160717.

Sequence in context: A304978 A078776 A188006 * A044338 A044719 A260202

Adjacent sequences: A160722 A160723 A160724 * A160726 A160727 A160728

Keyword

easy,nonn,base

Author

Omar E. Pol, Jun 12 2009

Status

approved