A244007 Semiprimes which are concatenation of three consecutive primes.

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

Author

K. D. Bajpai, Jun 17 2014

Keywords

• nonn
• base

Comments

The semiprimes in A132903.

Examples

			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.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to decimal expansion of n
• Index entries for sequences related to semiprimes

Crossrefs

Cf. A000040, A001358, A030469, A132903, A244057.

Programs

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