A279535 - OEIS

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A279535

Triangle read by rows: The number of digits in the smallest 9-repdigit that is a multiple of n and m, where n and m are coprime to 2 and 5.

1, 1, 1, 6, 6, 42, 1, 3, 6, 9, 2, 2, 6, 2, 22, 6, 6, 6, 6, 6, 78, 16, 16, 48, 16, 16, 48, 272, 18, 18, 18, 18, 18, 18, 144, 342, 6, 6, 42, 6, 6, 6, 48, 18, 42, 22, 22, 66, 22, 22, 66, 176, 198, 66, 506, 3, 9, 6, 27, 6, 6, 48, 18, 18, 66, 81, 28, 28, 84, 28, 28, 84, 112, 252, 84, 308, 84, 812

(list; table; graph; refs; listen; history; text; internal format)

OFFSET

1,4

COMMENTS

The number of digits of the smallest member of A002283 divisible by n and m, as n and m run through A045572. Numbers of the form 10^d-1 are not divisible through 5 or 2, so these are excluded in the table. Losely related to A278588.

LINKS

Table of n, a(n) for n=1..78.

FORMULA

T(i,j) = min{d: (n*m) | (10^d-1)} where n=A045572(i) and m=A045572(j).

EXAMPLE

The 3rd smallest number coprime to 2 and 5 is A045572(3)=7. The smallest 9-repdigit divisible by 7*7=49 is 10^42-1 = A002283(42), to T(3,3)=42.

The triangle starts

1, 1;

6, 6, 42;

1, 3, 6, 9;

2, 2, 6, 2, 22;

6, 6, 6, 6, 6, 78;