A156155 - OEIS

A156155

Numbers k such that prime(prime(k)) = 2 (mod prime(k)), where prime(k) = A000040(k) is the k-th prime.

%I #8 Feb 22 2020 03:43:10

%S 2,6,21,51892,1686970

%N Numbers k such that prime(prime(k)) = 2 (mod prime(k)), where prime(k) = A000040(k) is the k-th prime.

%F a(n) = A000720(A156154(n)).

%o (PARI) p=c=0; until(0, until( isprime(c++), p=nextprime(p+1)); (p-2)%c & next; print1( primepi(c)","))

%Y Cf. A023144, A156154.

%K nonn,more

%O 1,1

%A _M. F. Hasler_, Feb 04 2009

%E a(5) from _Jinyuan Wang_, Feb 22 2020