1,1

A000081(n) is prime for n = 3, 10, 15, 343, 387, 1087, ... a(4) = A000081(343) has 158 digits and is too large to be displayed here.

A000081(n) is semiprime for n = 4, 5, 8, 12, 16, 17, 27, 30, 38, 56, 63, 66, no more through n = 100.

Table of n, a(n) for n=1..3.

A000040 INTERSECTION A000081.

a(n) = A000081(A051420(n)). - Amiram Eldar, Nov 11 2017

A000081(30) = 354426847597 is not in the sequence because it is semiprime rather than prime: 23 * 15409862939.

Cf. A000040, A000041, A000055, A000081, A000169, A001858, A005200, A051420, A119641, A119642.

Sequence in context: A062665 A256669 A159564 * A119781 A028367 A000197

Adjacent sequences: A185664 A185665 A185666 * A185668 A185669 A185670

nonn,bref

Jonathan Vos Post, Feb 08 2011

approved