A346393 Irregular triangle read by rows: the n-th row gives the divisors of n ending with the final digit of n.
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, 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, 39, 10, 20, 40, 1, 41, 2, 42, 43, 4, 44, 5, 15, 45, 46, 47, 8, 48, 49, 10, 50
Offset: 1
Examples
The triangle begins: 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 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 39 10 20 40 ...
Links
- Stefano Spezia, First 5000 rows of the triangle, flattened
Programs
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Mathematica
r[n_]:=Drop[Select[Divisors[n],(Mod[#,10]==Mod[n,10]&)]]; Flatten[Array[r, 50]]
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PARI
row(n) = select(x->(x%10) == (n%10), divisors(n)); \\ Michel Marcus, Jul 25 2021
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Python
from sympy import divisors def auptorow(nn): for n in range(1, nn+1): yield from [d for d in divisors(n) if d%10 == n%10] print([an for an in auptorow(50)]) # Michael S. Branicky, Jul 21 2021