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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
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
Sequence in context: A304978 A078776 A188006 * A044338 A044719 A260202
KEYWORD
easy,nonn,base
AUTHOR
Omar E. Pol, Jun 12 2009
STATUS
approved

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Last modified March 29 00:26 EDT 2024. Contains 371264 sequences. (Running on oeis4.)