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.

A139220 Numbers k such that 41+(k+k^2)/2 = 41+A000217(k) is prime.

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%I A139220 #19 Sep 08 2022 08:45:33
%S A139220 0,3,11,20,23,27,32,39,44,48,51,56,59,60,83,104,108,111,116,128,132,
%T A139220 135,143,171,188,203,207,212,227,240,251,263,275,296,300,312,315,324,
%U A139220 356,359,363,380,384,392,399,408,443,447,476,479,483,504,507,515,527,528
%N A139220 Numbers k such that 41+(k+k^2)/2 = 41+A000217(k) is prime.
%C A139220 Corresponding values of primes are in A139219.
%C A139220 Numbers k such that both 41+(k+k^2)/2 and 41+(k+k^2) are primes, are in A139221.
%e A139220 If k = 11 then 41 + (k + k^2) / 2 = 107 (prime).
%t A139220 Select[Table[Range[0,1000]],PrimeQ[41+(#+#^2)/2]&]
%o A139220 (PARI) is(n)=isprime(n*(n+1)/2+41) \\ _Charles R Greathouse IV_, Aug 16 2015
%o A139220 (Magma) [k:k in [0..530]| IsPrime(41+(k+k^2) div 2)]; // _Marius A. Burtea_, Feb 12 2020
%Y A139220 Cf. A000217, A056561, A139219, A139221.
%K A139220 nonn
%O A139220 1,2
%A A139220 _Zak Seidov_, Apr 11 2008