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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

Table of n, a(n) for n=1..86.

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]<lpf[#-3]&](*A245024*)] (* Peter J. C. Moses, Aug 14 2014 *)

CROSSREFS

Cf. A245024, A243937, A242034, A020639.

Sequence in context: A123371 A011277 A084742 * A301738 A302387 A049613

Adjacent sequences:  A242030 A242031 A242032 * A242034 A242035 A242036

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Aug 12 2014

EXTENSIONS

More terms from Peter J. C. Moses, Aug 12 2014

STATUS

approved

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