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A160725 Cyclops semiprimes. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 26 07:31 EST 2022. Contains 350577 sequences. (Running on oeis4.)