A247476 A Skolem-type sequence: each pair of two terms that start with a digit k are separated by k other terms. Lexicographically earliest permutation of positive integers with this property.

1, 2, 10, 3, 20, 4, 5, 30, 6, 7, 40, 8, 50, 9, 11, 60, 12, 70, 21, 41, 80, 22, 23, 90, 42, 24, 13, 25, 14, 15, 26, 16, 17, 27, 18, 19, 28, 100, 29, 31, 43, 200, 51, 32, 61, 44, 33, 45, 52, 53, 34, 62, 46, 35, 47, 54, 55, 36, 63, 48, 37, 49, 56, 57, 38, 64, 400

Offset: 1

Author

Eric Angelini and M. F. Hasler, Nov 30 2014

Keywords

• nonn
• base
• nice

Examples

			The sequence starts 1,2,10,...: there is 1 term enclosed by 1 and 10: the term 2.
Then it goes on 1,2,10,3,20,...: there are 2 terms (10 and 3) enclosed between 2 and 20.
Then, in 1,2,10,3,20,4,5,30,... there are 3 terms (20, 4 and 5) enclosed by 3 and 30, etc.
		

Links

• Rémy Sigrist, Table of n, a(n) for n = 1..10000
• E. Angelini, A Skolem-like seq with no terms repeated, SeqFan list, Nov 22 2014
• Rémy Sigrist, Illustration of first terms
• Rémy Sigrist, PARI program for A247476

Programs

PARI

See Links section.

Extensions

Data corrected by Rémy Sigrist, Jul 10 2019