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 A242033 a(n)=lpf(A245024(n)-1), where lpf=least prime factor (A020639). 9
 3, 3, 3, 5, 3, 3, 3, 3, 7, 3, 5, 3, 3, 3, 3, 3, 5, 3, 7, 3, 3, 3, 3, 5, 3, 3, 3, 7, 3, 3, 5, 3, 3, 3, 3, 13, 3, 5, 3, 3, 3, 3, 3, 5, 3, 3, 3, 3, 3, 5, 3, 3, 3, 11, 3, 7, 3, 5, 3, 3, 3, 3, 3, 5, 3, 7, 3, 3, 3, 11, 3, 5, 3, 3, 3, 7, 3, 3, 5, 3, 19, 3, 3, 3, 3, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture. The sequence contains all odd primes. The conjecture is true.  Consider n-1 = p*q where p is an odd prime and q is a prime > p such that q == p^(-1) mod r for every odd prime r < p.  Such primes q exist by Dirichlet's theorem on primes in arithmetic progressions. - Robert Israel, Aug 13 2014 LINKS MAPLE lpf:= n -> min(numtheory:-factorset(n)): L:= [seq(lpf(2*i+1), i=1..1000)]: L[select(i->L[i] < L[i-1], [\$2..nops(L)])]; # Robert Israel, Aug 13 2014 MATHEMATICA lpf[n_]:=lpf[n]=First[First[FactorInteger[n]]]; (*lesat prime factor*)A242033=Map[lpf[#-1]&, Select[Range[6, 300, 2], lpf[#-1]

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Last modified October 23 20:17 EDT 2019. Contains 328373 sequences. (Running on oeis4.)