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 A081547 #12 Sep 03 2024 00:42:57
%S A081547 4,10,9,25,33,65,129,385,513,1025,2049,4097,8193,16385,32769,98305,
%T A081547 131073,262145,524289,1048577,2097153,4194305,8388609,16777217,
%U A081547 33554433,67108865,134217729,268435457,536870913,1073741825,2147483649
%N A081547 Smallest composite number which is 1 more than the product of n (not necessarily distinct) prime numbers.
%C A081547 a(2*n+1) = 2^(2*n+1)+1, n>0. - _Vladeta Jovovic_, Apr 02 2003
%H A081547 Harvey P. Dale, <a href="/A081547/b081547.txt">Table of n, a(n) for n = 1..1000</a>
%F A081547 For n>2, a(n) = 2^n+1 unless this is a Fermat prime (A019434), in which case a(n) = 2^(n-1)*3+1 (which is divisible by 5). - _Dean Hickerson_, Apr 05 2003
%t A081547 cno[n_]:=Module[{a=2^n+1},If[PrimeQ[a],2^(n-1)*3+1,a]]; Join[{4,10}, Array[cno,30,3]] (* _Harvey P. Dale_, Mar 24 2012 *)
%o A081547 (Python)
%o A081547 from sympy import isprime
%o A081547 def A081547(n): return 10 if n==2 else ((3<<n-1)+1 if isprime(m:=(1<<n)+1) else m) # _Chai Wah Wu_, Sep 02 2024
%Y A081547 Cf. A081545, A081546, A081548, A073919, A007583.
%K A081547 nonn
%O A081547 1,1
%A A081547 _Amarnath Murthy_, Apr 01 2003
%E A081547 More terms from _Vladeta Jovovic_, Apr 02 2003