%I #10 Feb 06 2021 21:52:52

%S 1,2,2,4,3,6,2,3,7,13,9,5,4,22,15,26,5,3,20,39,4,12,8,51,31,60,10,18,

%T 41,8,6,7,14,11,54,105,16,4,65,121,5,35,6,17,83,10,4,45,97,9,106,48,

%U 29,209,11,221,3,59,133,28,138,66,38,25,155,294,43,6,174,5

%N a(n) is the index k of the greatest prime divisor A002313(k) of n^2 + 1.

%C a(n) is the number k such that A002313(k) = A014442(n).

%H Michel Lagneau, <a href="/A248746/b248746.txt">Table of n, a(n) for n = 1..5000</a>

%e a(5)=3 because A002313(3)=13 and 5^2+1 = 2*13 with A002313(3)= A014442(5).

%p with(numtheory):T:=array(1..50000):T[1]:=2:kk:=1:nn:=10^5:

%p for i from 1 to nn do:

%p p:=4*i+1:

%p if type(p,prime)=true

%p then

%p kk:=kk+1:T[kk]:=p:

%p else

%p fi:

%p od:

%p for k from 1 to 5000 do:ii:=0:

%p y:=factorset(k^2+1):n2:=nops(y):t:=y[n2]:

%p for l from 1 to kk while(ii=0)do :

%p if t=T[l]

%p then

%p printf(`%d, `,l):

%p else

%p fi:

%p od:

%p od:

%Y Cf. A014442 (greatest prime divisor of n^2+1), A002313 (primes congruent to 1 or 2 modulo 4).

%Y Cf. also A002522.

%K nonn

%O 1,2

%A _Michel Lagneau_, Oct 13 2014