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A069558
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Triangular numbers in which the k-th digit, numbering them from right to left, either divides k or is a nonzero multiple of k. Is 1 only when k has no other single-digit divisor (less than 10).
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2
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1, 3, 6, 21, 28, 45, 66, 325, 666, 946, 2346, 2628, 2926, 8385, 8646, 52326, 54946
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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COMMENTS
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The n-th digit is 1 only when the smallest prime divisor of n is > 7.
Next term > 10^18. - Sascha Kurz, Mar 23 2002
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LINKS
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Table of n, a(n) for n=0..16.
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EXAMPLE
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8646 is a term in which, numbering the digits from right to left,
the 1st digit is 6;
the 2nd digit is 4, a multiple of 2;
the 3rd digit is 6, a multiple of 3;
the 4th digit is 8, a multiple of 4.
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CROSSREFS
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Cf. A000217, A069556, A069557, A069559.
Sequence in context: A173165 A210504 A101582 * A174461 A050611 A270510
Adjacent sequences: A069555 A069556 A069557 * A069559 A069560 A069561
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KEYWORD
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base,hard,more,nonn
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AUTHOR
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Amarnath Murthy, Mar 22 2002
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STATUS
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approved
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