A389477 - OEIS

%I #16 Oct 08 2025 16:08:29

%S 11,41,59,953

%N Primes p such that psi(p+3) = psi(p+4) = psi(p+5).

%C If it exists, a(5) > 4*10^10.

%e 11 is in the sequence since psi(11+3) = psi(11+4) = psi(11+5) = 24.

%t psi[n_] := psi[k] = n * Times @@ (1 + 1/FactorInteger[n][[;; , 1]]); psi[1] = 1; Select[Prime[Range[200]], psi[#+3] == psi[#+4] == psi[#+5] &] (* _Amiram Eldar_, Oct 05 2025 *)

%Y Cf. A000040, A001615, A119711, A387733, A389278.

%K nonn,hard,more

%O 1,1

%A _S. I. Dimitrov_, Oct 05 2025