A361988 a(n) is the least prime == 2*a(n-2) mod a(n-1); a(1) = 2, a(2) = 3.

2, 3, 7, 13, 53, 79, 659, 6089, 104831, 955657, 20278459, 103303609, 557074963, 1877832107, 2991982033, 6747646247, 12731610313, 179006226563, 10944843040969, 76971913739909, 98861599821847, 7568563814118343, 492154371117335989, 8381761436622948499, 177001298911316590457, 6919814180414592924821

Offset

1,1

Comments

The sequence of least primes == 2*a(n-1) mod a(n-2), starting with a(1) = 2 and a(2) = 3, is 2, 3, 2, 7, 2, 11, 2, 37, 2, 41, 2, 127, 2, 131, ..., the interleaving of 2 and A362005.

Links

Robert Israel, Table of n, a(n) for n = 1..391

Example

a(4) = 13 because 13 is the first prime == 2*3 (mod 7).

Maple

A[1]:= 2: A[2]:= 3:
for i from 3 to 30 do
  for k from 2*A[i-2] mod A[i-1] by A[i-1] do
    if isprime(k) then A[i]:= k; break fi
  od
od:
seq(A[i], i=1..30);

Crossrefs

Cf. A362005.

Sequence in context: A257393 A273814 A371131 * A085872 A070858 A061067

Adjacent sequences: A361985 A361986 A361987 * A361989 A361990 A361991

Keyword

nonn

Author

Robert Israel, Apr 02 2023

Status

approved