OFFSET
1,2
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..500
EXAMPLE
42 is in the sequence because the prime divisors of 42 are 2, 3, 7 and 1/2 + 1/3 + 1/7 + 1/(2*3*7) = 1.
MAPLE
with(numtheory):for n from 1 to 5000 do: x:=factorset(n):n1:=nops(x): d:= sum('1/x[i] ', 'i'=1..n1) + product('1/x[j] ', 'j'=1..n1):if d=1 then printf(`%d, `, n):else fi:od:
MATHEMATICA
pdd1Q[n_]:=Module[{c=FactorInteger[n][[All, 1]]}, Total[1/c]+ 1/Times@@c ==1]; Join[{1}, Select[Range[1500], pdd1Q]] (* Harvey P. Dale, Aug 22 2016 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Michel Lagneau, Jul 04 2013
STATUS
approved