A385959 a(0) = 1; a(n) = a(n-1)*(b(n)+1)/(b(n)-1), where b(n) = A385958(n) is the largest prime p such that a(n) is an integer.

1, 2, 3, 4, 6, 7, 14, 15, 16, 18, 19, 38, 57, 76, 114, 115, 120, 121, 132, 135, 136, 138, 139, 278, 279, 310, 312, 314, 471, 628, 942, 1099, 2198, 2199, 2932, 4398, 5131, 10262, 10995, 10996, 16494, 19243, 38486, 41235, 41236, 41358, 41471, 41838, 41841, 46490, 55788, 55789, 111578, 167367, 168554, 252831, 252832, 252864

Offset

0,2

Comments

a(0) = 1; a(n) is the smallest k such that (k + a(n-1))/(k - a(n-1)) is a prime (A385958).

Note that a(n-1)+1 <= a(n) <= 2*a(n-1).

Links

Martin Fuller, Table of n, a(n) for n = 0..3460

Formula

a(n) = Product_{k=1..n} (b(k)+1)/(b(k)-1), where b(n) = A385958(n).

a(n) = (1+t(n))/(1-t(n)) with t(n) = tanh(Sum_{k=1..n} arctanh(1/b(k))).

Crossrefs

Cf. A385958.

Sequence in context: A380193 A096477 A039059 * A151892 A162570 A073639

Adjacent sequences: A385956 A385957 A385958 * A385960 A385961 A385962

Keyword

nonn,look

Author

Thomas Ordowski, Jul 13 2025

Extensions

More terms from Morné Louw and Martin Fuller, Jul 15 2025

Status

approved