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A246447 The odd primes squared plus 1 and the composites squared minus 1.

%I A246447 #28 May 22 2025 10:21:40
%S A246447 10,15,26,35,50,63,80,99,122,143,170,195,224,255,290,323,362,399,440,
%T A246447 483,530,575,624,675,728,783,842,899,962,1023,1088,1155,1224,1295,
%U A246447 1370,1443,1520,1599,1682,1763,1850,1935,2024,2115,2210,2303,2400,2499,2600
%N A246447 The odd primes squared plus 1 and the composites squared minus 1.
%C A246447 The odd primes squared plus 1 and the nonprimes squared minus 1 are the numerators or denominators of an infinite product converging to 1 whose denominators or numerators, conversely, are the squares of said numbers, that is, (p^2+1/p^2)*(q^2-1)/q^2)..., where p is an odd prime and q is a nonprime.
%C A246447 Union of A066872 and (A062312 - 1) with 0 and 5 removed. - _Robert Israel_, Aug 26 2014
%H A246447 Jens Kruse Andersen, <a href="/A246447/b246447.txt">Table of n, a(n) for n = 1..10000</a>
%o A246447 (PARI) lista(nn) = {for (n=3, nn, if (isprime(n), print1(n^2+1, ", "), print1(n^2-1, ", ")););} \\ _Michel Marcus_, Aug 26 2014
%o A246447 (Python)
%o A246447 for n in range(3,10**3):
%o A246447   if isprime(n):
%o A246447     print(n**2+1,end=', ')
%o A246447   else:
%o A246447     print(n**2-1,end=', ') # _Derek Orr_, Sep 19 2014
%Y A246447 Cf. A066872, A062312.
%K A246447 nonn,easy
%O A246447 1,1
%A A246447 _Leo Depuydt_, Aug 26 2014
%E A246447 More terms from _Michel Marcus_, Aug 26 2014