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A173381 a(n) = b_n(p_(n+1)) where p_n is the n-th prime, b_n(1)=1, b_n(2)=p_n, and for k>=3, b_n(k) is the smallest number larger than b_n(k-1) such that, for all i<k, b_n(k) is relatively prime to b_n(i) iff k is relatively prime to i. 0
3, 11, 31, 163, 661, 929, 2041, 21341, 15989, 47387, 125117, 263411, 123493, 10426601, 3654221, 4167127, 86622397, 4036267, 3910993, 541513877 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..20.

MAPLE

b:= proc(n, k) option remember; local ok, m, i;

      if k=1 then 1

    elif k=2 then ithprime(n)

    else for m from b(n, k-1)+1 do

           ok:= true;

           for i from 1 to k-1 do

             if igcd(k, i)=1 xor igcd(m, b(n, i))=1

                then ok:= false; break fi

           od;

           if ok then break fi

         od; m

      fi

    end:

a:= n-> b(n, ithprime(n+1));

seq(a(n), n=1..10);  # Alois P. Heinz, Nov 22 2010

CROSSREFS

Cf. A000040, A172980, A172999.

Sequence in context: A146456 A095692 A163421 * A076477 A319335 A104079

Adjacent sequences:  A173378 A173379 A173380 * A173382 A173383 A173384

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Nov 22 2010

EXTENSIONS

More terms from Alois P. Heinz, Nov 22 2010

STATUS

approved

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Last modified September 18 23:16 EDT 2020. Contains 337174 sequences. (Running on oeis4.)