A106554 Concatenation of the two prime divisors of a semiprime, smallest divisor first.

22, 23, 33, 25, 27, 35, 37, 211, 55, 213, 311, 217, 57, 219, 313, 223, 77, 317, 511, 319, 229, 231, 513, 323, 237, 711, 241, 517, 243, 329, 713, 331, 247, 519, 253, 337, 523, 259, 717, 1111, 261, 341, 343, 719, 267, 347, 271, 1113

Offset

1,1

Comments

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

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Formula

a(n) = A037276(A001358(n)). - R. J. Mathar, Oct 29 2012

Example

First semiprime is 4; 4 is 2*2 -> 22.
Second semiprime is 6; 6 is 2*3 -> 23.
Third semiprime is 9; 9 is 3*3 -> 33.
Fourth semiprime is 10; 10 is 2*5 -> 25.

Maple

read("transforms") :
A106554 := proc(n)
    A037276(A001358(n)) ;
end proc: # R. J. Mathar, Oct 29 2012

Mathematica

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

Prog

(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

Crossrefs

Cf. A106550, A084126, A084127, A001358.

Sequence in context: A114963 A146755 A106556 * A118297 A022392 A041976

Adjacent sequences: A106551 A106552 A106553 * A106555 A106556 A106557

Keyword

base,easy,nonn

Author

Eric Angelini, May 09 2005

Extensions

More terms from Reinhard Zumkeller, May 19 2005

Data corrected by Giovanni Teofilatto and Altug Alkan, Oct 01 2015

Status

approved