A061017 -id:A061017 - cp's OEIS frontend

A228363 Sorted entries of the multiplication table a*b, with a>1, b>1.

4, 6, 6, 8, 8, 9, 10, 10, 12, 12, 12, 12, 14, 14, 15, 15, 16, 16, 16, 18, 18, 18, 18, 20, 20, 20, 20, 21, 21, 22, 22, 24, 24, 24, 24, 24, 24, 25, 26, 26, 27, 27, 28, 28, 28, 28, 30, 30, 30, 30, 30, 30, 32, 32, 32, 32, 33, 33, 34, 34, 35, 35, 36, 36, 36, 36, 36, 36, 36, 38, 38, 39, 39, 40, 40, 40, 40

Offset: 1

Ralf Stephan, Aug 21 2013

nonn

Consists of the composite numbers (A002808), with the composite nonsquares (A089229) occurring more than once, i.e., the n-th composite appears A144925(n) times.

A complement of the primes (A000040).

Cf. A061017 (sorted entries of standard multiplication table)

L=listcreate();for(k=2,250,for(l=2,250,listput(L,k*l)));v=vecsort(Vec(L));for(n=1,100,print1(v[n],","))

A319135 Irregular triangle read by rows in which row n lists the positive divisors of n that are <= sqrt(n) in decreasing order.

Original entry on oeis.org

1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 1, 3, 2, 1, 1, 2, 1, 3, 1, 4, 2, 1, 1, 3, 2, 1, 1, 4, 2, 1, 3, 1, 2, 1, 1, 4, 3, 2, 1, 5, 1, 2, 1, 3, 1, 4, 2, 1, 1, 5, 3, 2, 1, 1, 4, 2, 1, 3, 1, 2, 1, 5, 1, 6, 4, 3, 2, 1, 1, 2, 1, 3, 1, 5, 4, 2, 1, 1, 6, 3, 2, 1

Offset: 1

Charles Kusniec, Feb 27 2021

Reversing rows gives A161906.

			Triangle begins:
1
1
1
2 1
1
2 1
1
2 1
3 1
2 1
1
3 2 1
1
2 1
3 1
4 2 1

Cf. A038548 (row widths), A033676 (first column), A333750 (second column), A161906 (rows reversed), A027750, A056538, A061017, A340791, A340792.

row(n) = Vecrev(select(x->(x<=sqrt(n)), divisors(n))); \\ Jinyuan Wang, Mar 13 2021

a(n) * A161908(n) = A340792(n)
A161906(n) * A340791(n) = A340792(n)
A027750(n) * A056538(n) = A061017(n)

More terms from Jinyuan Wang, Mar 13 2021

cp's OEIS Frontend

A228363 Sorted entries of the multiplication table a*b, with a>1, b>1.

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