A392217 - OEIS

%I #10 Jan 07 2026 21:14:47

%S 1,1,1,2,1,2,1,2,4,1,2,1,2,3,6,1,2,4,1,2,3,6,1,2,4,1,2,5,10,1,2,4,1,2,

%T 3,4,6,12,1,2,3,6,1,2,4,8,1,2,4,8,1,2,4,8,16,1,2,3,6,1,2,3,6,9,18,1,2,

%U 4,8,1,2,3,4,6,12,1,2,5,10,1,2,11,22,1,2,4,8,1,2,4,5,10,20

%N Irregular triangle read by rows: the n-th row gives the divisors of phi(n).

%H Stefano Spezia, <a href="/A392217/b392217.txt">Table of n, a(n) for n = 1..13241</a> (first 1000 rows of the triangle)

%H <a href="/index/Di#divisors">Index entries for sequences related to divisors of numbers</a>.

%e The irregular triangle begins as:

%e   1;

%e   1;

%e   1, 2;

%e   1, 2;

%e   1, 2, 4;

%e   1, 2;

%e   1, 2, 3,  6;

%e   1, 2, 4;

%e   1, 2, 3,  6;

%e   1, 2, 4;

%e   1, 2, 5, 10;

%e   1, 2, 4;

%e   1, 2, 3,  4, 6, 12;

%e   ...

%t row[n_]:=Divisors[EulerPhi[n]]; Array[row,25]//Flatten

%Y Cf. A000010, A000012 (1st column), A027750, A062402 (row sums), A392218 (row products).

%K nonn,easy,look,tabf

%O 1,4

%A _Stefano Spezia_, Jan 03 2026