A074852 - OEIS

%I #20 May 13 2013 01:54:06

%S 9,25,27,81,125,6561,24389,59049,161051,357911,571787,1442897,4782969,

%T 5177717,14348907,18191447,30080231,73560059,80062991,118370771,

%U 127263527,131872229,318611987,344472101,440711081,461889917,590589719

%N Composite n such that n and n+2 are prime powers.

%H Charles R Greathouse IV, <a href="/A074852/b074852.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) list(lim)=my(v=List(),t);lim+=.5;for(e=2,log(lim)\log(3), forprime(p=3, lim^(1/e),ispower(t=p^e+2,,&t); if(isprime(t), listput(v,p^e)))); vecsort(Vec(v))

%o \\ _Charles R Greathouse IV_, Apr 30 2012

%o (PARI) list(lim)=my(v=List());if(lim>=25,listput(v,25));lim+=.5;for(e=2, log(lim)\log(3), forprime(p=3, lim^(1/e),if(isprime(p^e+2), listput(v, p^e)))); vecsort(Vec(v))

%o /* This second program assumes A076427(2) = 1 but is about a hundred times faster. I proved that it is correct up to 10^20 without this assumption. */

%o \\ _Charles R Greathouse IV_, Apr 30 2012

%Y Cf. A006549, A053702.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Sep 10 2002

%E More terms from _Sascha Kurz_, Jan 30 2003