A192281 - OEIS

%I #5 Mar 30 2012 18:53:49

%S 5,7,11,17,19,29,43,47,61,71,79,89,101,107,109,151,191,197,223,251,

%T 271,317,349,359,421,439,461,521,569,601,631,659,673,691,701,719,811,

%U 821,881,911,919,947,971,991,1009,1051,1091,1109,1153,1181,1217,1231

%N Prime numbers whose anti-divisors are all prime numbers

%e Anti-divisors of 109 are 2, 3, 7, 31, 73 that are all prime numbers

%p with(numtheory);

%p P:=proc(i)

%p local a,b,c,k,j,n,ok;

%p for n from 3 by 1 to i do

%p   j:=ithprime(n); a:={};

%p    for k from 2 to j-1 do

%p      if abs((j mod k)- k/2) < 1 then a:=a union {k}; fi;

%p    od;

%p    b:=nops(a); c:=op(a);

%p    if b>1 then

%p      ok:=1;

%p      for k from 1 to b do

%p        if (not isprime(c[k])) then ok:=0; break; fi;

%p      od;

%p      if ok=1 then print(j); fi;

%p    else

%p      if isprime(op(a)) then print(j); fi;

%p    fi;

%p od;

%p end:

%Y Cf. A066272

%K nonn,easy

%O 1,1

%A _Paolo P. Lava_, Jul 15 2011