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Irregular triangle read by rows: the n-th row gives the divisors of n ending with the final digit of n.
1

%I #38 Mar 05 2022 11:07:24

%S 1,2,3,4,5,6,7,8,9,10,1,11,2,12,13,14,5,15,16,17,18,19,10,20,1,21,2,

%T 22,23,4,24,5,25,26,27,28,29,10,30,1,31,2,32,3,33,34,5,35,6,36,37,38,

%U 39,10,20,40,1,41,2,42,43,4,44,5,15,45,46,47,8,48,49,10,50

%N Irregular triangle read by rows: the n-th row gives the divisors of n ending with the final digit of n.

%H Stefano Spezia, <a href="/A346393/b346393.txt">First 5000 rows of the triangle, flattened</a>

%e The triangle begins:

%e 1

%e 2

%e 3

%e 4

%e 5

%e 6

%e 7

%e 8

%e 9

%e 10

%e 1 11

%e 2 12

%e 13

%e 14

%e 5 15

%e 16

%e 17

%e 18

%e 19

%e 10 20

%e 1 21

%e 2 22

%e 23

%e 4 24

%e 5 25

%e 26

%e 27

%e 28

%e 29

%e 10 30

%e 1 31

%e 2 32

%e 3 33

%e 34

%e 5 35

%e 6 36

%e 37

%e 38

%e 39

%e 10 20 40

%e ...

%t r[n_]:=Drop[Select[Divisors[n],(Mod[#,10]==Mod[n,10]&)]]; Flatten[Array[r, 50]]

%o (Python)

%o from sympy import divisors

%o def auptorow(nn):

%o for n in range(1, nn+1):

%o yield from [d for d in divisors(n) if d%10 == n%10]

%o print([an for an in auptorow(50)]) # _Michael S. Branicky_, Jul 21 2021

%o (PARI) row(n) = select(x->(x%10) == (n%10), divisors(n)); \\ _Michel Marcus_, Jul 25 2021

%Y Cf. A010879, A027750, A330348 (row length).

%K nonn,tabf,base

%O 1,2

%A _Stefano Spezia_, Jul 21 2021