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a(n) is the smallest positive number k such that k^2 - 1 and k^2 + 1 each have exactly n distinct prime divisors.
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%I #35 Oct 05 2023 14:27:50

%S 2,5,13,83,463,4217,169333,2273237,23239523,512974197,5572561567

%N a(n) is the smallest positive number k such that k^2 - 1 and k^2 + 1 each have exactly n distinct prime divisors.

%F a(n) >= max(A219017(n), A180278(n)). - _Daniel Suteu_, Sep 03 2023

%o (PARI) isok(k, n) = (omega(k^2-1)==n) && (omega(k^2+1)==n);

%o a(n) = my(k=2); while (!isok(k, n), k++); k; \\ _Michel Marcus_, Sep 03 2023

%Y Cf. A001221, A180278, A219017.

%Y Cf. A088075 (with k instead of k^2).

%K nonn,more

%O 1,1

%A _Juri-Stepan Gerasimov_, Sep 01 2023

%E a(9)-a(11) from _Amiram Eldar_, Sep 03 2023