cp's OEIS Frontend

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.

A217286 Larger of pairs of emirps (A006567) whose difference with the (smaller) reversal is a triangular number (A000217).

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%I A217286 #31 Jan 30 2023 19:31:38
%S A217286 73,1811,7817,7927,11701,12611,14431,14831,15101,15241,15541,15601,
%T A217286 16111,16451,16651,17021,18671,18731,19181,19541,19681,19841,32213,
%U A217286 32713,33223,33623,33923,35803,36013,36353,36913,37123,37363,37463,37963,39383,39983,71707
%N A217286 Larger of pairs of emirps (A006567) whose difference with the (smaller) reversal is a triangular number (A000217).
%C A217286 Related to A217386 as triangular numbers (A000217) are to squares (A000290), but in the current sequence, only the larger of each emirp pair is used.
%H A217286 Alois P. Heinz, <a href="/A217286/b217286.txt">Table of n, a(n) for n = 1..100</a>
%F A217286 {k: k is in A006567 and k - A004086(k) is in A000217}.
%e A217286 a(1) = 73 because 73 - 37 = 36 = 8th triangular number.
%e A217286 a(2) = 1811 because R(1811) = A004086(1811) = 1181, and 1811 - 1181 = 630 = 35th triangular number.
%e A217286 a(3) = 7817 because 7817 - 7187 = 630 = 35th triangular number.
%e A217286 a(4) = 7927 because 7927 - 7297 = 630 = 35*36/2.
%t A217286 emrp[p_]:=Module[{rev=IntegerReverse[p]},If[rev!=p&&PrimeQ[rev],Max[ rev,p],Nothing]]; Select[Union[emrp/@Prime[Range[7500]]],OddQ[Sqrt[8(#-IntegerReverse[ #])+1]]&] (* _Harvey P. Dale_, Jan 30 2023 *)
%Y A217286 Cf. A000217, A004086, A006567, A217386.
%K A217286 nonn,base,easy
%O A217286 1,1
%A A217286 _Jonathan Vos Post_, Oct 02 2012
%E A217286 More terms from _Alois P. Heinz_, Oct 03 2012