A122443 Least prime factor of powers of semiprimes.
1, 2, 2, 3, 2, 2, 3, 2, 3, 2, 5, 2, 3, 2, 5, 2, 2, 3, 2, 7, 3, 5, 3, 2, 2, 2, 5, 3, 2, 7, 3, 2, 5, 2, 3, 7, 3, 2, 5, 2, 2, 3, 5, 2, 7, 11, 2, 3, 3, 7, 2, 3, 2, 11, 5, 2, 5, 2, 3, 7, 2, 13, 3, 2, 3, 5, 11, 2, 2, 3, 2, 7, 5, 2, 11, 3, 2, 5, 2, 7, 2, 3, 13, 3, 2, 5, 3, 13
Offset: 1
Links
- Michael De Vlieger, Table of n, a(n) for n = 1..10000
Crossrefs
Programs
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Mathematica
FactorInteger[#][[1, 1]] & /@ Select[Range@ 250, Function[n, Or[n == 1, And[Length@ # == 1, EvenQ@ First@ #], And[Length@ # == 2, SameQ @@ #]] &[FactorInteger[n][[All, -1]]]]] (* Michael De Vlieger, Mar 04 2017 *)
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PARI
is(n)=my(f=factor(n)[, 2]); #f==0 || (#f==2 && f[1]==f[2]) || (#f==1 && f[1]%2==0); spf(n) = if (n==1, 1, factor(n)[1,1]); lista(nn) = {for (n=1, nn, if (is(n), print1(spf(n), ", ")););} \\ Michel Marcus, Mar 04 2017
Extensions
More terms from Michel Marcus, Mar 04 2017