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.
a(n)={t=0; forstep(m=2, 10^n, 2, if(!(m%3)==0, x=0; until(p<2||isprime(p), p=m-3^x; x++); if(p<2, t++))); return(t)};
Do[ i = 0; l = Ceiling[ N[ Log[ 3, n ] ] ]; While[ ! PrimeQ[ n - 3^i ] && i < l, i++ ]; If[ i == l, Print[ n ] ], {n, 2, 1000, 2} ]
isok(n) = {if (n % 2, 0, lim = log(n)/log(3); for (k=0, lim, if (isprime(n - 3^k), return (0)););1;);} \\ Michel Marcus, Feb 25 2017
a(14) = 3; 14 - 3^0 = 13, 14 - 3 = 11, 14 - 3^2 = 5, three primes.
lst:=[]; for n in [1..105] do c:=0; e:=Floor(Log(3, n)); k:=0; while k le e do p:=n-3^k; if IsPrime(p) then c+:=1; end if; k+:=1; end while; Append(~lst, c); end for; lst;
A282432 := proc(n) a := 0 ; for k from 0 do if n-3^k < 2 then return a ; elif isprime(n-3^k) then a := a+1 ; end if; end do: end proc: seq(A282432(n),n=1..80) ; # R. J. Mathar, Mar 07 2022
ispp3(n) = (n==1) || (n==3) || (ispower(n,,&p) && (p==3));
a(n) = {my(nb = 0); forprime(p=2, n, nb += ispp3(n-p);); nb;} \\ Michel Marcus, Feb 18 2017
lst:=[]; for n in [2..62] do k:=n+2; t:=0; while t eq 0 do if GCD(k, n) eq 1 and GCD(k-1, n-1) eq 1 then x:=-1; repeat x+:=1; p:=k-n^x; until p lt 2 or IsPrime(p); if p lt 2 then Append(~lst, k); t:=1; end if; end if; k+:=1; end while; end for; lst;
lst:=[]; for n in [3..143433 by 6] do c:=0; e:=Floor(Log(3, n)); m:=0; while m le e do a:=n-3^m; if IsPrime(a+1) or IsPrime(a-1) then break; end if; c+:=1; m+:=1; end while; if c eq e+1 then Append(~lst, n); end if; end for; lst;
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