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A069558 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). 2
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)
OFFSET

0,2

COMMENTS

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

LINKS

Table of n, a(n) for n=0..16.

EXAMPLE

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.

CROSSREFS

Cf. A000217, A069556, A069557, A069559.

Sequence in context: A173165 A210504 A101582 * A174461 A050611 A270510

Adjacent sequences: A069555 A069556 A069557 * A069559 A069560 A069561

KEYWORD

base,hard,more,nonn

AUTHOR

Amarnath Murthy, Mar 22 2002

STATUS

approved

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Last modified January 29 06:03 EST 2023. Contains 359915 sequences. (Running on oeis4.)