cp's OEIS Frontend

A357127 a(n) = A081257(n) if A081257(n) > n, otherwise a(n) = 1.

%I A357127 #21 Oct 15 2022 21:16:10
%S A357127 7,13,7,31,43,19,73,13,37,19,157,61,211,241,1,307,1,127,421,463,1,79,
%T A357127 601,31,37,757,271,67,1,331,151,1123,397,97,43,67,1483,223,547,1723,
%U A357127 139,631,283,109,103,61,181,1,2551,379,919,409,2971,79,103,3307,163,3541,523,97,3907,109,73,613
%N A357127 a(n) = A081257(n) if A081257(n) > n, otherwise a(n) = 1.
%C A357127 All the primes in this sequence appear exactly twice.
%C A357127 The new primes encountered seem to match the terms of A256148 for n>1. _Bill McEachen_, Oct 13 2022
%F A357127 Conjecture 1: If a(n) != 1, then a(n) = a(a(n) - n - 1).
%F A357127 Conjecture 2: If n != m and a(n) = a(m), then
%F A357127 a(n) = gcd(n^2 + n + 1, m^2 + m + 1) = n + m + 1.
%e A357127 a(2) = a(a(2) - 2 - 1) = a(7 - 2 - 1) = a(4).
%e A357127 a(3) = a(9) = 3 + 9 + 1 = 13.
%e A357127 a(5) = a(25) = gcd(5^2 + 5 + 1, 25^2 + 25 + 1) = 31.
%o A357127 (Python)
%o A357127 from sympy import primefactors
%o A357127 def A357127(n): return m if (m:=max(primefactors(n*(n+1)+1))) > n else 1 # _Chai Wah Wu_, Oct 15 2022
%Y A357127 Cf. A081257, A081256, A108768, A256148.
%K A357127 nonn
%O A357127 2,1
%A A357127 _Mohammed Bouras_, Sep 13 2022