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 A279946 #29 Jul 06 2021 16:12:20
%S A279946 1,10396,326656,2619897841,82318050361,660219495802336,
%T A279946 20744313326831116,166376633378560463881,5227608446905776928921,
%U A279946 41927244364003774523222476,1317367783816405284315203776,10565749434051302554022550018121,331979316252074156011094205115681
%N A279946 Numbers that are both dodecagonal and centered heptagonal.
%C A279946 From _Jon E. Schoenfield_, Dec 24 2016: (Start)
%C A279946 Intersection of dodecagonal numbers A051624 and centered heptagonal numbers A069099. A051624(j) = j(5j - 4), A069099(k) = (7*k^2 - 7^k + 2)/2, and the table below gives indices j and k at which A051624(j) = A069099(k):
%C A279946 .
%C A279946 n a(n) j k
%C A279946 = ================= ======== ========
%C A279946 1 1 1 0, 1
%C A279946 2 10396 46 55
%C A279946 3 326656 256 306
%C A279946 4 2619897841 22891 27360
%C A279946 5 82318050361 128311 153361
%C A279946 6 660219495802336 11491036 13734415
%C A279946 7 20744313326831116 64411666 76986666
%C A279946 ... (End)
%D A279946 F. Tapson (1999). The Oxford Mathematics Study Dictionary (2nd ed.). Oxford University Press. pp. 88-89.
%H A279946 Colin Barker, <a href="/A279946/b279946.txt">Table of n, a(n) for n = 1..350</a>
%H A279946 Wikipedia, <a href="https://en.wikipedia.org/wiki/Polygonal_number">Polygonal number</a>
%H A279946 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,252002,-252002,-1,1).
%F A279946 Empirical: a(1)=1, a(2)=10396, a(3)=326656, a(4)=2619897841, a(n) = 252002*a(n-2) - a(n-4) + 85050 for n > 4. - _Jon E. Schoenfield_, Dec 24 2016
%F A279946 G.f.: x*(1 + 10395*x + 64258*x^2 + 10395*x^3 + x^4) / ((1 - x)*(1 - 502*x + x^2)*(1 + 502*x + x^2)). - _Colin Barker_, Dec 24 2016
%e A279946 From _Jon E. Schoenfield_, Dec 24 2016: (Start)
%e A279946 10396 is both the 46th dodecagonal number and the 55th centered heptagonal number: A051624(46) = 46(5*46 - 4) = 10396 and A069099(55) = (7*55^2 - 7*55 + 2)/2 = 10396.
%e A279946 A051624(256) = 256(5*256 - 4) = 326656 = (7*306^2 - 7*306 + 2)/2 = A069099(306). (End)
%t A279946 LinearRecurrence[{1,252002,-252002,-1,1},{1,10396,326656,2619897841,82318050361},20] (* _Harvey P. Dale_, Jul 06 2021 *)
%o A279946 (PARI) Vec(x*(1 + 10395*x + 64258*x^2 + 10395*x^3 + x^4) / ((1 - x)*(1 - 502*x + x^2)*(1 + 502*x + x^2)) + O(x^20)) \\ _Colin Barker_, Dec 24 2016
%Y A279946 Cf. dodecagonal numbers A051624, centered heptagonal numbers A069099.
%K A279946 nonn,easy
%O A279946 1,2
%A A279946 _Ann Skoryk_, Dec 23 2016