[seqfan] Question regarding A069570

Jeremy Gardiner jeremy.gardiner at btinternet.com
Thu Jun 17 12:17:23 CEST 2010


I may be missing something, but some terms of A069570 (Numbers in which the
n-th digit is either a divisor or a multiple of n) appear to be incorrect:

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 19, 18, 19, 21, 22, 23,
24, 25, 26, 27, 28, 29, 41, 42, 43, 44, 45, 46, 47, 48, 49, 61, 62, 63, 64,
65, 66, 67, 68, 69, 81, 82, 83, 84, 85, 86, 87, 88, 89, 111, 121, 122, 123,
124, 125, 126, 127, 128, 129, 141, 142, 143

My interpretation is that,

1st digit is either a divisor or a multiple of 1,
2nd digit is either a divisor or a multiple of 2,
3rd digit is either a divisor or a multiple of 3, etc.

e.g. Why are 13 and 122 in the sequence, among others?

Regards,
Jeremy Gardiner






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