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

1,2

Comments

Sequence is a permutation of the positive integers.

Links

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

Example

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.

Crossrefs

Cf. A113982.

Sequence in context: A217559 A217560 A114112 * A234519 A289726 A308598

Adjacent sequences: A113978 A113979 A113980 * A113982 A113983 A113984

Keyword

nonn

Author

Leroy Quet, Nov 11 2005

Extensions

More terms from Diana L. Mecum, May 29 2007

More terms from Diana L. Mecum, Aug 15 2008

Status

approved