login
A244007
Semiprimes which are concatenation of three consecutive primes.
2
235, 71113, 192329, 232931, 293137, 535961, 616771, 677173, 737983, 798389, 838997, 107109113, 137139149, 149151157, 181191193, 191193197, 211223227, 223227229, 233239241, 257263269, 269271277, 277281283, 337347349, 349353359, 373379383, 421431433, 431433439
OFFSET
1,1
COMMENTS
The semiprimes in A132903.
EXAMPLE
235 is in the sequence because concatenation of [2, 3, 5] = 235 = 5 * 47, which is semiprime.
71113 is in the sequence because concatenation of [7, 11, 13] = 71113 = 7 * 10159, which is semiprime.
111317 is not in the sequence because, though 111317 is concatenation of three consecutive primes [11, 13, 17], but it is not semiprime.
MAPLE
with(numtheory): with(StringTools): A244007:= proc() local a, b, c, k, m; a:=ithprime(n); b:=ithprime(n+1); c:=ithprime(n+2); m:=parse(cat(a, b, c)); k:=bigomega(m); if (k)=2 then RETURN (m); fi; end: seq(A244007 (), n=1..100);
MATHEMATICA
A244007 = {}; Do[t = FromDigits[Flatten[IntegerDigits /@ {Prime[n], Prime[n + 1], Prime[n + 2]}]]; If [PrimeOmega[t] == 2, AppendTo[A244007, t]], {n, 100}]; A244007
CROSSREFS
KEYWORD
nonn,base
AUTHOR
K. D. Bajpai, Jun 17 2014
STATUS
approved