A176170 Smallest prime-factor of n-th product of 4 distinct primes.

2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2

Offset

1,1

Comments

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

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Formula

a(n) = A020639(A046386(n)). - Antti Karttunen, Dec 06 2017

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, f1[n]]], {n, 0, 2*7!}]; lst

Prog

(PARI) n=0; i=0; while(i<10000, n++; if((4 == bigomega(n))&&(4 == omega(n)), i++; write("b176170.txt", i, " ", factor(n)[1, 1]))); \\ Antti Karttunen, Dec 06 2017

Crossrefs

Cf. A020639, A046386, A006881, A007304, A070647, A096916, A096917, A096918, A096919

Sequence in context: A105514 A214081 A194338 * A062153 A217693 A204560

Adjacent sequences: A176167 A176168 A176169 * A176171 A176172 A176173

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Apr 10 2010

Status

approved