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A135646 a(m, n) is the number of coprime pairs (i, j) with 1 <= i <= m, 1 <= j <= n; table of a(m, n) read by antidiagonals. 0
1, 2, 2, 3, 3, 3, 4, 5, 5, 4, 5, 6, 7, 6, 5, 6, 8, 9, 9, 8, 6, 7, 9, 12, 11, 12, 9, 7, 8, 11, 13, 15, 15, 13, 11, 8, 9, 12, 16, 16, 19, 16, 16, 12, 9, 10, 14, 18, 20, 21, 21, 20, 18, 14, 10, 11, 15, 20, 22, 26, 23, 26, 22, 20, 15, 11, 12, 17, 22, 25, 29, 29, 29, 29, 25, 22, 17, 12 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A kind of 2-dimensional version of the Euler phi function A000010.

LINKS

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

FORMULA

a(n, n) = 2 sum_1^n{ phi(i) } - 1 = 2 A002088(n) - 1 = A018805(n).

a(m, n) <= mn - sum_1^m{ (i - phi(i)) floor(n / i) }

Conjecture: a(m, n) ~ mn - sum_1^m{ (i - phi(i)) (n / i) } = n sum_1^m{ phi(i) / i } ~ 6mn / pi^2 as m -> oo.

EXAMPLE

a(2, 5) = 8 since of the 10 possible pairs all but (2, 2) and (2, 4) are coprime

The terms given correspond to the following values:

1 = a(1, 1)

2 2 = a(2, 1), a(1, 2)

3 3 3 = a(3, 1), a(2, 2), a(1, 3), etc

4 5 5 4

5 6 7 6 5

6 8 9 9 8 6

7 9 12 11 12 9 7

8 11 13 15 15 13 11 8

9 12 16 16 19 16 16 12 9

10 14 18 20 21 21 20 18 14 10

etc

CROSSREFS

Cf. A000010 (Euler's totient function), A002088 (sum of totient function), A018805.

Sequence in context: A124882 A262518 A085578 * A101646 A166079 A269381

Adjacent sequences:  A135643 A135644 A135645 * A135647 A135648 A135649

KEYWORD

nonn,tabl

AUTHOR

Hugo van der Sanden, Nov 22 2008

STATUS

approved

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Last modified June 25 00:41 EDT 2017. Contains 288708 sequences.