A074852 Composite n such that n and n+2 are prime powers.

9, 25, 27, 81, 125, 6561, 24389, 59049, 161051, 357911, 571787, 1442897, 4782969, 5177717, 14348907, 18191447, 30080231, 73560059, 80062991, 118370771, 127263527, 131872229, 318611987, 344472101, 440711081, 461889917, 590589719

Offset: 1

Author

Benoit Cloitre, Sep 10 2002

Keywords

• nonn

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006549, A053702.

Programs

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))
\\ Charles R Greathouse IV, Apr 30 2012

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))
/* 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. */
\\ Charles R Greathouse IV, Apr 30 2012

Extensions

More terms from Sascha Kurz, Jan 30 2003