A074320 a(n) = sum of smallest and largest prime factors of n, for n>1; a(1)=2.

2, 4, 6, 4, 10, 5, 14, 4, 6, 7, 22, 5, 26, 9, 8, 4, 34, 5, 38, 7, 10, 13, 46, 5, 10, 15, 6, 9, 58, 7, 62, 4, 14, 19, 12, 5, 74, 21, 16, 7, 82, 9, 86, 13, 8, 25, 94, 5, 14, 7, 20, 15, 106, 5, 16, 9, 22, 31, 118, 7, 122, 33, 10, 4, 18, 13, 134, 19, 26, 9, 142, 5, 146, 39, 8, 21, 18, 15

Offset: 1

Author

Jason Earls, Sep 26 2002

Keywords

• easy
• nonn

Comments

If n is prime, a(n) = 2n; the only prime factor, n itself, is taken as both the "smallest" and "largest" prime factor of n. - Jon E. Schoenfield, Jan 14 2015

Links

• R. Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A046665, A066048, A130064, A130065.

Programs

Mathematica

f[n_]:=Transpose[FactorInteger[n]][[1]];Table[First[f[n]]+Last[f[n]],{n,200}] (* Vladimir Joseph Stephan Orlovsky, Apr 08 2011 *)

PARI

a(n) = if (n==1, 2, my(f=factor(n)); f[1,1] + f[#f~,1]); \\ Michel Marcus, Jan 14 2015

Formula

a(n) = A020639(n) + A006530(n).