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).

1, 3, 6, 21, 28, 45, 66, 325, 666, 946, 2346, 2628, 2926, 8385, 8646, 52326, 54946

Offset

1,2

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=1..17.

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,changed

Author

Amarnath Murthy, Mar 22 2002

Extensions

Offset corrected by Sean A. Irvine, May 04 2024

Status

approved