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A176172 3rd prime-factor of n-th product of 4 distinct primes. 2
5, 5, 5, 7, 5, 7, 5, 5, 7, 7, 7, 11, 5, 7, 5, 7, 5, 11, 7, 7, 7, 5, 11, 5, 7, 13, 7, 7, 5, 11, 13, 11, 7, 5, 7, 7, 5, 7, 13, 7, 5, 11, 11, 17, 7, 7, 11, 5, 7, 11, 11, 5, 11, 7, 5, 13, 7, 13, 17, 5, 7, 13, 11, 13, 7, 5, 11, 7, 7, 11, 19, 5, 11, 11, 7, 11, 7, 13, 5, 11, 17, 7, 13, 11, 7, 5, 7, 7, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

FactorInteger[210]=2*3*5*7,...

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

N:= 10000: # to use products <= N

Primes:= select(isprime, [2, seq(i, i=3..N/30)]):

P4:= NULL:

for ia from 1 to nops(Primes) do

  a:= Primes[ia];

  for ib from 1 to ia-1 do

    b:= Primes[ib];

    if 6*a*b > N then break fi;

    for ic from 1 to ib-1 do

      c:= Primes[ic];

      if 2*a*b*c > N then break fi;

      for id from 1 to ic-1 do

        d:= Primes[id];

        if a*b*c*d > N then break fi;

        R[a*b*c*d]:= b;

        P4:= P4, a*b*c*d;

od od od od:

P4:= sort([P4]):

map(t -> R[t], P4); # Robert Israel, May 14 2019

MATHEMATICA

f0[n_]:=Last/@FactorInteger[n]=={1, 1, 1, 1}; f1[n_]:=Min[First/@FactorInteger[n]]; f2[n_]:=First/@FactorInteger[n][[2, 1]]; f3[n_]:=First/@FactorInteger[n][[3, 1]]; f4[n_]:=Max[First/@FactorInteger[n]]; lst={}; Do[If[f0[n], AppendTo[lst, f3[n]]], {n, 0, 2*7!}]; lst

CROSSREFS

Cf. A006881, A007304, A070647, A096916, A096917, A096918, A096919, A176170, A176171

Sequence in context: A127934 A205236 A266948 * A204911 A087516 A194428

Adjacent sequences:  A176169 A176170 A176171 * A176173 A176174 A176175

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Apr 10 2010

STATUS

approved

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Last modified December 12 07:00 EST 2019. Contains 329948 sequences. (Running on oeis4.)