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 A115908 #22 Dec 08 2024 11:09:39
%S A115908 1,5,6,15,23,141,150,258,317,340,359,378,471,503,768,1363,2175,2516,
%T A115908 3285,3342,3815,3905,4385,4748,5385,5976,6026,6900,7048,7151,7411,
%U A115908 7698,8251,8310,8828,10182,10461,12022,12508,13722,13840,15456,16582
%N A115908 Numbers k such that phi(k) + prime(k) is a triangular number.
%H A115908 Amiram Eldar, <a href="/A115908/b115908.txt">Table of n, a(n) for n = 1..10000</a>
%e A115908 phi(503) + prime(503) = 4095 = T(90).
%t A115908 With[{trnos = Accumulate[Range[5000]]}, Select[Range[20000], MemberQ[trnos, (EulerPhi[#] + Prime[#])] &]] (* _Harvey P. Dale_, Jan 12 2011 *)
%t A115908 Select[Range[20000],OddQ[Sqrt[8(EulerPhi[#]+Prime[#])+1]]&] (* _Harvey P. Dale_, Dec 08 2024 *)
%o A115908 (PARI) isok(n) = ispolygonal(prime(n) + eulerphi(n), 3); \\ _Michel Marcus_, Jan 25 2014
%Y A115908 Cf. A000010, A115882, A115907.
%K A115908 nonn
%O A115908 1,2
%A A115908 _Giovanni Resta_, Feb 06 2006