A211271
Number of integer pairs (x,y) such that 0
0, 0, 1, 1, 1, 1, 1, 2, 1, 2, 1, 3, 1, 2, 2, 3, 1, 2, 1, 4, 2, 2, 1, 4, 2, 2, 2, 4, 1, 4, 1, 4, 2, 2, 3, 4, 1, 2, 2, 6, 1, 4, 1, 4, 3, 2, 1, 6, 2, 4, 2, 4, 1, 3, 3, 6, 2, 2, 1, 7, 1, 2, 3, 5, 3, 4, 1, 4, 2, 6, 1, 6, 1, 2, 4, 4, 3, 4, 1, 8, 2, 2, 1, 7, 3, 2, 2, 6, 1, 6, 3, 4, 2, 2, 3, 7, 1, 4, 3, 7, 1, 4, 1, 6, 5, 2, 1, 6
Offset: 1
Keywords
Examples
a(3) counts this pair: (3,3). - _Antti Karttunen_, Jan 15 2025 a(20) counts these pairs: (3,20), (4,15), (5,12), (6,10).
Links
- Antti Karttunen, Table of n, a(n) for n = 1..20000
Programs
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Mathematica
a = 1; b = n; z1 = 120; t[n_] := t[n] = Flatten[Table[x*y, {x, a, b - 1}, {y, x, b}]] c[n_, k_] := c[n, k] = Count[t[n], k] Table[c[n, n], {n, 1, z1}] (* A038548 *) Table[c[n, n + 1], {n, 1, z1}] (* A072670 *) Table[c[n, 2*n], {n, 1, z1}] (* A211270 *) Table[c[n, 3*n], {n, 1, z1}] (* A211271 *) Table[c[n, Floor[n/2]], {n, 1, z1}] (* A211272 *) c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, a, m}] Print Table[c1[n, n], {n, 1, z1}] (* A094820 *) Table[c1[n, n + 1], {n, 1, z1}] (* A091627 *) Table[c1[n, 2*n], {n, 1, z1}] (* A211273 *) Table[c1[n, 3*n], {n, 1, z1}] (* A211274 *) Table[c1[n, Floor[n/2]], {n, 1, z1}] (* A211275 *) -
PARI
A211271(n) = { my(n3=3*n); sumdiv(n3,d,(d <= (n3/d) && (n3/d) <= n)); }; \\ Antti Karttunen, Jan 15 2025
Extensions
Data section extended up to a(108) and a(3) corrected from 0 to 1 by Antti Karttunen, Jan 15 2025
Comments