cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-1 of 1 results.

A283626 Number of integer triples (x,y,z), x > 0, y > 0, z > 0, such that x <= p, y <= q, z <= r for any factorization n = p*q*r.

Original entry on oeis.org

1, 4, 7, 13, 13, 25, 19, 38, 37, 49, 31, 74, 37, 73, 79, 104, 49, 125, 55, 143, 121, 121, 67, 203, 121, 145, 171, 221, 85, 263, 91, 272, 205, 193, 199, 354, 109, 217, 247, 383, 121, 398, 127, 377, 381, 265, 139, 531, 253, 443, 331, 455, 157, 558, 355, 587, 373
Offset: 1

Views

Author

Rémy Sigrist, Mar 12 2017

Keywords

Comments

This sequence is a three-dimensional equivalent of A138808.
a(n) >= 3*n-2, with equality iff n is not composite.
a(n) >= 3*A138808(n)-3*n+1, with equality iff n has at most 2 prime factors (counted with multiplicity).

Crossrefs

Cf. A138808.

Programs

  • PARI
    a(n)=my(h=matrix(n,n)); fordiv(n,d, fordiv(n/d,dd, for(x=1,d, for(y=1,dd,h[x,y]=max(h[x,y],n/d/dd))))); return(sum(x=1,n, sum(y=1,n,h[x,y])))
Showing 1-1 of 1 results.