OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
MATHEMATICA
ok[1]=True; ok[n_]:=And@@(Mod[#, 7]==1&)/@FactorInteger[n][[All, 1]]; Select[Range[6000], ok] (* Vincenzo Librandi, Aug 20 2012 *)
PROG
(Magma) [n: n in [1..2000] | forall{d: d in PrimeDivisors(n) | d mod 7 eq 1}]; // Vincenzo Librandi, Aug 20 2012
(PARI) is(n)=if(n%7!=1, return(0)); my(f=factor(n)[, 1]); for(i=1, #f~, if(f[i]%7!=1, return(0))); 1 \\ Charles R Greathouse IV, Jul 02 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved