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 A117416 #11 Jun 10 2024 16:22:32
%S A117416 4,4,9,26,82,247,731,2186,6559,19679,59047,177149,531439,1594322,
%T A117416 4782979,14348905,43046722,129140159,387420493,1162261465,3486784399,
%U A117416 10460353201,31381059597,94143178823,282429536489,847288609441
%N A117416 Semiprime nearest to 3^n. In case of a tie, choose the smaller.
%C A117416 See also: A117405 Semiprime nearest to 2^n. A117387 Prime nearest to 2^n.
%F A117416 a(n) = 3^n + A117416(n). a(n) = 3^n + Min{k such that A001358(i) + k = 3^n}.
%e A117416 a(0) = 4 because 3^0 + 3 = 4 = A001358(1) and no semiprime is closer to 3^0.
%e A117416 a(1) = 4 because 3^1 + 1 = 4 = A001358(1) and no semiprime is closer to 3^1.
%e A117416 a(2) = 9 because 3^2 + 0 = 9 = 3^2 = A001358(3), no semiprime is closer to 3^2.
%e A117416 a(3) = 26 because 3^3 - 1 = 26 = 2 * 13, no semiprime is closer.
%e A117416 a(4) = 82 because 3^4 + 1 = 82 = 2 * 41, no semiprime is closer.
%e A117416 a(5) = 247 because 3^5 + 4 = 247 = 13 * 19, no semiprime is closer.
%t A117416 nsp[n_]:=Module[{c=3^n,a,b,j=1,k=1},While[PrimeOmega[c-j]!=2,j++]; a=c-j;While[ PrimeOmega[ c+k]!=2,k++];b=c+k;If[(b-c)<(c-a),b,a]]; Join[ {4,4,9}, Array[nsp,30,3]] (* _Harvey P. Dale_, Apr 11 2015 *)
%Y A117416 Cf. A000079, A001358, A117387, A117405, A117406, A117416.
%K A117416 easy,nonn,less
%O A117416 0,1
%A A117416 _Jonathan Vos Post_, Mar 13 2006