A244007 - OEIS

%I #12 Jun 19 2014 11:49:40

%S 235,71113,192329,232931,293137,535961,616771,677173,737983,798389,

%T 838997,107109113,137139149,149151157,181191193,191193197,211223227,

%U 223227229,233239241,257263269,269271277,277281283,337347349,349353359,373379383,421431433,431433439

%N Semiprimes which are concatenation of three consecutive primes.

%C The semiprimes in A132903.

%H K. D. Bajpai, <a href="/A244007/b244007.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/De#decimal_expansion">Index entries for sequences related to decimal expansion of n</a>

%H <a href="/index/Se#semiprime">Index entries for sequences related to semiprimes</a>

%e 235 is in the sequence because concatenation of [2, 3, 5] = 235 = 5 * 47, which is semiprime.

%e 71113 is in the sequence because concatenation of [7, 11, 13] = 71113 = 7 * 10159, which is semiprime.

%e 111317 is not in the sequence because, though 111317 is concatenation of three consecutive primes [11, 13, 17], but it is not semiprime.

%p 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);

%t A244007 = {}; Do[t = FromDigits[Flatten[IntegerDigits /@ {Prime[n], Prime[n + 1], Prime[n + 2]}]]; If  [PrimeOmega[t] == 2,  AppendTo[A244007, t]], {n, 100}]; A244007

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

%K nonn,base

%O 1,1

%A _K. D. Bajpai_, Jun 17 2014