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 A259040 #11 Dec 03 2019 21:13:30
%S A259040 12,15,21,33,60,75,84,93,123,186,264,327,384,519,651,654,678,726,753,
%T A259040 762,771,807,831,852,870,897,924,975,993,1023,1029,1056,1110,1122,
%U A259040 1128,1149,1194,1203,1248,1257,1272,1290,1302,1308,1317,1347,1407,1437,1443,1464,1482,1524,1527,1533,1554,1581,1644,1662,1677
%N A259040 Numbers n such that digital root of n is 3*(digital root of n-th prime).
%C A259040 Corresponding primes:
%C A259040 37, 47, 73, 137, 281, 379, 433, 487, 677, 1109, 1693, 2179, 2657, 3719, 4861, 4889, 5077, 5501, 5717, 5807, 5861, 6203, 6373, 6581, 6761, 6977, 7229, 7687, 7867, 8147, 8209, 8443, 8929, 9029, 9091, 9281, 9677, 9749, 10163, 10253, 10369, 10567, 10667, 10729, 10837, 11117, 11719, 11981.
%C A259040 Conjecture: a(n) ~ 27n. - _Charles R Greathouse IV_, Jun 18 2015
%C A259040 All terms are divisible by 3 but not by 9. - _Robert Israel_, Dec 03 2019
%H A259040 Robert Israel, <a href="/A259040/b259040.txt">Table of n, a(n) for n = 1..10000</a>
%p A259040 droot:= n -> subs(0=9, n mod 9):
%p A259040 select(t -> droot(t) = 3*droot(ithprime(t)), [seq(i,i=3..10000,3)]); # _Robert Israel_, Dec 03 2019
%t A259040 Reap[Do[If[FixedPoint[Total[IntegerDigits[#]]&,n]==3*Mod[Prime[n], 9], Sow[{n,Prime[n]}]],{n,2000}]][[2,1]]
%o A259040 (PARI) n=0; forprime(p=2, 1e4, if(p%9*3==n++%9, print1(n", "))) \\ _Charles R Greathouse IV_, Jun 18 2015
%Y A259040 Cf. A010888, A038194, A258876, A258877, A259032.
%K A259040 nonn,base
%O A259040 1,1
%A A259040 _Zak Seidov_, Jun 17 2015