A176172 - OEIS

A176172

3rd prime-factor of n-th product of 4 distinct primes.

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

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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