A248746 - OEIS

A248746

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

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, 41, 8, 6, 7, 14, 11, 54, 105, 16, 4, 65, 121, 5, 35, 6, 17, 83, 10, 4, 45, 97, 9, 106, 48, 29, 209, 11, 221, 3, 59, 133, 28, 138, 66, 38, 25, 155, 294, 43, 6, 174, 5

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OFFSET

1,2

COMMENTS

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

LINKS

Michel Lagneau, Table of n, a(n) for n = 1..5000

EXAMPLE

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

MAPLE

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

for i from 1 to nn do:

p:=4*i+1:

if type(p, prime)=true

then

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

else

fi:

od:

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

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

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

if t=T[l]

then

printf(`%d, `, l):

else

fi:

od:

CROSSREFS

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

Cf. also A002522.

Sequence in context: A357189 A241450 A189675 * A227154 A324655 A275735

Adjacent sequences: A248743 A248744 A248745 * A248747 A248748 A248749

KEYWORD

nonn

AUTHOR

Michel Lagneau, Oct 13 2014

STATUS

approved