A113981 a(1)=1. a(n) is smallest positive integer that does not occur earlier in the sequence and is such that d(a(n)) does not equal d(a(n-1)), where d(n) is the number of positive divisors of n.

1, 2, 4, 3, 6, 5, 8, 7, 10, 9, 12, 11, 14, 13, 16, 15, 18, 17, 20, 19, 23, 24, 21, 22, 26, 25, 28, 27, 30, 29, 32, 31, 36, 37, 40, 33, 34, 41, 42, 35, 38, 39, 44, 43, 46, 45, 48, 47, 50, 49, 52, 51, 54, 53, 56, 55, 59, 60, 57, 58, 62, 61, 64, 63, 66, 65, 68, 67, 70, 69, 72, 71

Offset: 1

Author

Leroy Quet, Nov 11 2005

Keywords

• nonn

Comments

Sequence is a permutation of the positive integers.

Examples

			Since d(a(4)) = d(3) = 2, d(a(5)) cannot be 2. a(5)= 6 is the smallest positive integer not occurring earlier in the sequence where d(a(5)) is not 2, since d(6) = 4.
		

Links

• Diana Mecum, Table of n, a(n) for n = 1..1195 [From _Diana L. Mecum_, Aug 15 2008]

Crossrefs

Cf. A113982.

Extensions

More terms from Diana L. Mecum, May 29 2007

More terms from Diana L. Mecum, Aug 15 2008