1,3

The integers coprime to 5 are 1,2,3,4,6,.. The a(1)th=1st of these is 1. The integers coprime to 4 are 1,3,5,.. The a(2)th=1st of these is 1. The integers coprime to 3 are 1,2,4,5,.. The a(3)th=2nd of these is 2. The integers coprime to 2 are 1,3,5,7,9,.. The a(4)th=4th of these is 7. And the integers coprime to 1 are 1,2,3,4,5,6,7,8,9,10,.. The a(5)th=9th of these is 9. So a(6) = 1 + 1 + 2 + 7 + 9 = 20.

Cf. A132273, A132274, A132275.

Sequence in context: A001385 A039808 A138164 this_sequence A022543 A036618 A003018

Adjacent sequences: A130799 A130800 A130801 this_sequence A130803 A130804 A130805

more,nonn

Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Aug 20 2007