This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A208247 #17 Mar 01 2019 03:16:33 %S A208247 2,3,119,127,163,179,191,193,217,219,221,223,239,251,269,311,337,343, %T A208247 389,403,415,419,427,431,457,491,505,547,557,569,575,581,583,597,599, %U A208247 613,653,659,667,671,673,683,697,719,739,749,767,779,787,799,807,817 %N A208247 Numbers having exactly one partition into two prime powers. %C A208247 A071330(a(n)) = 1. %H A208247 Reinhard Zumkeller, <a href="/A208247/b208247.txt">Table of n, a(n) for n = 1..10000</a> %o A208247 (Haskell) %o A208247 a095841 n = a095841_list !! (n-1) %o A208247 a095841_list = filter ((== 1) . a071330) a000961_list %o A208247 (PARI) is(n)=sum(i=2,n\2,isprimepower(i)&&isprimepower(n-i))+isprimepower(n-1)==1 || n==2 \\ naive; _Charles R Greathouse IV_, Nov 21 2014 %o A208247 (PARI) is(n)=my(s); forprime(p=2,n\2,if(isprimepower(n-p) && s++>1, return(0))); for(e=2,log(n)\log(2), forprime(p=2, sqrtnint(n\2,e), if(isprimepower(n-p^e) && s++>1,return(0)))); s+(!!isprimepower(n-1))==1 || n==2 \\ faster; _Charles R Greathouse IV_, Nov 21 2014 %Y A208247 A095841 = Intersection of A208247 and A000961. %K A208247 nonn %O A208247 1,1 %A A208247 _Reinhard Zumkeller_, Jan 11 2013