

A176172


3rd primefactor of nth 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
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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 ia1 do
b:= Primes[ib];
if 6*a*b > N then break fi;
for ic from 1 to ib1 do
c:= Primes[ic];
if 2*a*b*c > N then break fi;
for id from 1 to ic1 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



