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Concatenation of the two prime divisors of a semiprime, smallest divisor first.
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%I #24 Feb 06 2024 14:27:21

%S 22,23,33,25,27,35,37,211,55,213,311,217,57,219,313,223,77,317,511,

%T 319,229,231,513,323,237,711,241,517,243,329,713,331,247,519,253,337,

%U 523,259,717,1111,261,341,343,719,267,347,271,1113

%N Concatenation of the two prime divisors of a semiprime, smallest divisor first.

%C Concatenation of the divisors starting with the largest one leads to another sequence.

%H Michael De Vlieger, <a href="/A106554/b106554.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A037276(A001358(n)). - _R. J. Mathar_, Oct 29 2012

%e First semiprime is 4; 4 is 2*2 -> 22.

%e Second semiprime is 6; 6 is 2*3 -> 23.

%e Third semiprime is 9; 9 is 3*3 -> 33.

%e Fourth semiprime is 10; 10 is 2*5 -> 25.

%p read("transforms") :

%p A106554 := proc(n)

%p A037276(A001358(n)) ;

%p end proc: # _R. J. Mathar_, Oct 29 2012

%t FromDigits@ Flatten[IntegerDigits@ Table[#1, {#2}] & @@@ FactorInteger@ #] & /@ Select[Range@ 144, PrimeOmega@ # == 2 &] (* _Michael De Vlieger_, Oct 01 2015 *)

%o (PARI) do(x)=my(v=List()); forprime(p=2, sqrt(x), forprime(q=p, x\p, listput(v, [p*q, eval(Str(p, q))]))); Vec(apply(u->u[2], vecsort(v, 1))) \\ _Charles R Greathouse IV_, Sep 30 2015

%Y Cf. A106550, A084126, A084127, A001358.

%K base,easy,nonn

%O 1,1

%A _Eric Angelini_, May 09 2005

%E More terms from _Reinhard Zumkeller_, May 19 2005

%E Data corrected by _Giovanni Teofilatto_ and _Altug Alkan_, Oct 01 2015