A198067 Square array read by antidiagonals, n>=1, k>=1; T(n,k) is the number of nonprime numbers which are prime to n and are not strong divisors of k.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 3, 1, 2, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 1, 3, 1, 2, 1, 1, 1, 1, 2, 3, 1, 2, 1, 2, 1, 1, 1, 1, 6, 2, 3, 1, 3, 1, 2, 1, 1, 1, 1, 1, 6, 2, 2, 1, 2, 1, 1, 1, 1, 1, 1, 7, 1, 6, 2, 3, 1, 3, 1, 2

Offset: 1

Author

Peter Luschny, Nov 07 2011

Keywords

• nonn
• tabl

Comments

We say d is a strong divisor of n iff d is a divisor of n and d > 1. Let alpha(n) be number of nonprime numbers in the reduced residue system of n. Then alpha(n) = T(n,1) = T(n,n).

Examples

			T(15, 22) = card({1,4,8,14}) = 4 because the coprimes of 15 are {1,2,4,7,8,11,13,14} and the strong divisors of 22 are {2,11,22}.
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[x][1][2][3][4][5][6][7][8]
[1] 1, 1, 1, 1, 1, 1, 1, 1
[2] 1, 1, 1, 1, 1, 1, 1, 1
[3] 1, 1, 1, 1, 1, 1, 1, 1
[4] 1, 1, 1, 1, 1, 1, 1, 1
[5] 2, 2, 2, 1, 2, 2, 2, 1
[6] 1, 1, 1, 1, 1, 1, 1, 1
[7] 3, 3, 3, 2, 3, 2, 3, 2
[8] 1, 1, 1, 1, 1, 1, 1, 1
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Triangle k=1..n, n>=1:
[1]           1
[2]          1, 1
[3]        1, 1, 1
[4]       1, 1, 1, 1
[5]     2, 2, 2, 1, 2
[6]    1, 1, 1, 1, 1, 1
[7]  3, 3, 3, 2, 3, 2, 3
[8] 1, 1, 1, 1, 1, 1, 1, 1
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Triangle n=1..k, k>=1:
[1]           1
[2]          1, 1
[3]        1, 1, 1
[4]       1, 1, 1, 1
[5]     1, 1, 1, 1, 2
[6]    1, 1, 1, 1, 2, 1
[7]  1, 1, 1, 1, 2, 1, 3
[8] 1, 1, 1, 1, 1, 1, 2, 1
		

Links

• Peter Luschny, Euler's totient function

Crossrefs

Cf. A000010, A048864, A193804, A193805, A198066.

Programs

Maple

strongdivisors := n -> numtheory[divisors](n) minus {1}:
coprimes  := n -> select(k->igcd(k, n)=1, {$1..n}):
nonprimes := n -> remove(isprime, {$1..n});
T := (n,k) -> nops(nonprimes(n) intersect (coprimes(n) minus strongdivisors(k))):
seq(seq(T(n-k+1, k), k=1..n), n=1..13);  # Square array by antidiagonals.
seq(print(seq(T(n,k), k=1..n)), n=1..8); # Lower triangle.
seq(print(seq(T(n,k), n=1..k)), k=1..8); # Upper triangle.