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A106554 Concatenation of the two prime divisors of a semiprime, smallest divisor first. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Concatenation of the divisors starting with the largest one leads to another sequence.
LINKS
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)
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
Sequence in context: A114963 A146755 A106556 * A118297 A022392 A041976
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

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Last modified March 29 05:16 EDT 2024. Contains 371264 sequences. (Running on oeis4.)