A391788 Array read by antidiagonals: A(n,k) = phi(n+k) with k >= 0 and A(0,0) = 0.

0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 4, 4, 4, 4, 4, 4, 2, 2, 2, 2, 2, 2, 2, 6, 6, 6, 6, 6, 6, 6, 6, 4, 4, 4, 4, 4, 4, 4, 4, 4, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4

Offset

0,7

Links

Table of n, a(n) for n=0..90.

Example

The array begins:
  0, 1, 1, 2, 2,  4,  2,  6, ...
  1, 1, 2, 2, 4,  2,  6,  4, ...
  1, 2, 2, 4, 2,  6,  4,  6, ...
  2, 2, 4, 2, 6,  4,  6,  4, ...
  2, 4, 2, 6, 4,  6,  4, 10, ...
  4, 2, 6, 4, 6,  4, 10,  4, ...
  2, 6, 4, 6, 4, 10,  4, 12, ...
  ...

Mathematica

A[n_, k_]:=EulerPhi[n+k]; Table[A[n-k, k], {n, 0, 12}, {k, 0, n}]//Flatten

Crossrefs

Cf. A062570 (main diagonal), A391789, A391790.

A002618 + A000010 gives the antidiagonal sums.

Sequence in context: A032572 A237975 A327343 * A032574 A058515 A126696

Adjacent sequences: A391785 A391786 A391787 * A391789 A391790 A391791

Keyword

nonn,easy,tabl

Author

Stefano Spezia, Dec 20 2025

Status

approved