A061285 a(n) = 2^((prime(n) - 1)/2).

2, 4, 8, 32, 64, 256, 512, 2048, 16384, 32768, 262144, 1048576, 2097152, 8388608, 67108864, 536870912, 1073741824, 8589934592, 34359738368, 68719476736, 549755813888, 2199023255552, 17592186044416, 281474976710656, 1125899906842624, 2251799813685248

Offset: 2

Author

Labos Elemer, May 22 2001

Keywords

• nonn

Comments

Square root of 2^(prime(n) - 1), i.e., the smallest number that has prime(n) divisors.

Links

• Index to divisibility sequences

Crossrefs

Cf. A000005, A000010, A005097, A005179, A006005, A006093, A034785, A217054.

Programs

Mathematica

Table[2^((Prime[n] - 1)/2), {n, 2, 25}] (* Amiram Eldar, Dec 23 2020 *)

Formula

a(n) = sqrt(min(x; A000005(x) = prime(n))) = sqrt(A034785(n)/2) = sqrt(2^(prime(n) - 1)) = sqrt(2^A006093(n)) = sqrt(2^phi(prime(n))) = sqrt(2^A000010(A000040(n))).

Sum_{n>=1} 1/a(n) = A217054. - Amiram Eldar, Dec 23 2020