A241007 - OEIS

%I #11 Aug 16 2014 18:18:41

%S 3,6,7,8,13,19,20,31,35,38,40,43,44,45,56,60,63,65,68,69,96,97,103,

%T 104,109,116,119,122,125,133,138,151,157,159,160,171,174,181,189,193,

%U 204,209,211,212,215,216,220,221,232,241,248,250,254,267,271,273,280

%N Decimal encoding of the prime factorization of a(n) is a prime.

%C This sequence gives all arguments for which A067599 is prime: A067599(a(n)) = prime. - _Wolfdieter Lang_, Aug 16 2014

%H Paolo P. Lava, <a href="/A241007/b241007.txt">Table of n, a(n) for n = 1..1000</a>

%F Sequence of the members of the set {k >= 2: A067599(k) is a prime} in increasing order. - _Wolfdieter Lang_, Aug 16 2014

%e Prime factorization of a(4) = 8 is 2^3 and its decimal encoding is A067599(8) = 23 that is prime.

%e Prime factorization of a(188) = 994 is 2^1*7^1*71^1 and its decimal encoding is  A067599(994) = 2171711 that is prime.

%p with(numtheory); P:=proc(q) local a,b,c,d,k,j,n;

%p for n from 1 to q do a:=(ifactors(n)[2]); b:=[];

%p for k from 1 to nops(a) do b:=[op(b),a[k,1]]; od; b:=sort(b); c:=0;

%p for k from 1 to nops(b) do d:=1; while b[k]<>a[d,1] do d:=d+1; od;

%p j:=b[k]*10^(ilog10(a[d,2])+1)+a[d,2];

%p c:=c*10^(ilog10(j)+1)+j; od; if isprime(c) then print(n);

%p fi; od; end: P(1000);

%Y Cf. A067598, A067599.

%K nonn,easy,base

%O 1,1

%A _Paolo P. Lava_, Aug 07 2014

%E Edited: Name n-> a(n), cf. A067599, examples specified. - _Wolfdieter Lang_, Aug 16 2014