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 A218123 Denominators of terms of the sequence {c(n)} defined in A218121. 2
 1, 2, 2, 2, 2, 3, 3, 3, 5, 5, 5, 7, 7, 7, 7, 7, 7, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 17, 17, 17, 17, 17, 17, 19, 19, 19, 19, 19, 19, 19, 23, 23, 23, 23, 23, 23, 23, 23, 29, 29, 29, 29, 31, 31, 31, 31, 31, 31, 31, 31, 31, 37, 37, 37, 37, 37, 37, 41, 41, 41, 41, 43, 43, 43, 43, 43, 43, 43, 47, 47 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS It is easy to see that every prime is in the sequence. LINKS MAPLE ispfree := proc(a, b)     local alow ;     alow := floor(a);     if nextprime(alow) < b then         false;     else         true;     end if; end proc: A218121c := proc(n)     option remember;     local k ;     if n = 1 then         return 1;     elif n = 2 then         return 5/2 ;     else         if ispfree(ithprime(n)/procname(n-1), ithprime(n+1)/procname(n-1)) then             return procname(n-1) ;         end if ;         for k from n by -1 do             if ispfree( ithprime(n)*ithprime(k)/ithprime(n+1), ithprime(k) )                 and ithprime(n+1)/ithprime(k) > procname(n-1) then                 return ithprime(n+1)/ithprime(k) ;             end if;         end do:     end if; end proc: A218123 := proc(n)     denom(A218121c(n)) ; end proc: # R. J. Mathar, Dec 02 2012 CROSSREFS Cf. A218121, A217871, A217689, A217691, A217833, A217884. Sequence in context: A029084 A032229 A024366 * A288157 A333701 A140682 Adjacent sequences:  A218120 A218121 A218122 * A218124 A218125 A218126 KEYWORD nonn,frac AUTHOR Vladimir Shevelev, Oct 21 2012 STATUS approved

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Last modified May 18 22:37 EDT 2022. Contains 353826 sequences. (Running on oeis4.)