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 A077721 #15 Sep 07 2018 03:51:46 %S A077721 7,2801,17207,19559,120401,134513,134807,137201,840743,842759,842801, %T A077721 941249,943601,958007,958049,958343,960793,5782001,5784409,5899307, %U A077721 5899601,5899657,5901659,6591089,6607903,6706393,6708787,6722801,6722857,6723193 %N A077721 Primes which can be expressed as sum of distinct powers of 7. %C A077721 Primes whose base 7 representation contains only zeros and 1's. %H A077721 Robert Israel, <a href="/A077721/b077721.txt">Table of n, a(n) for n = 1..10000</a> %p A077721 pos := 0:for i from 1 to 4000 do b := convert(i,base,2); s := sum(b[j]*7^(j-1),j=1..nops(b)): if(isprime(s)) then pos := pos+1:a[pos] := s:fi: od:seq(a[j],j=1..pos); %t A077721 Select[Prime[Range[10^6]], Max[IntegerDigits[#, 7]]<=1 &] (* _Vincenzo Librandi_, Sep 07 2018 *) %Y A077721 Cf. A020449, A000695, A033044, A077717, A077718, A077719, A077720, A077722, A077723. %K A077721 nonn %O A077721 1,1 %A A077721 _Amarnath Murthy_, Nov 19 2002 %E A077721 More terms from _Sascha Kurz_, Jan 03 2003