A063721 Number of proper divisors of n is a square and sets a new record for such squares.

1, 2, 16, 48, 6480, 331776, 26542080, 207360000, 174142586880, 5476584960000, 8352895346933760000, 2556424320523960320000, 190741334440500264960000, 40745645800296001044480000, 11921333402531266560000000000000000, 58061203494913461453027322869401518080000

Offset

1,2

Links

Sean A. Irvine, Table of n, a(n) for n = 1..18

Sean A. Irvine, Java program (github)

Prog

(PARI) a=-1; for(n=1, 10^7, x=numdiv(n)-1; if(issquare(x), b=x; if(b>a, a=b; print(n))))
(PARI) {a063721(m)=local(r, n, x); r=-1; for(n=1, m, x=numdiv(n)-1; if(issquare(x) && x>r, r=x; print1(n, ", "))) }

Crossrefs

Cf. A032741.

Sequence in context: A162442 A159010 A223219 * A232209 A012180 A058376

Adjacent sequences: A063718 A063719 A063720 * A063722 A063723 A063724

Keyword

nonn

Author

Jason Earls, Aug 22 2001

Extensions

More terms from Don Reble, May 12 2002

Missing a(12) inserted and a(16) from Sean A. Irvine, May 09 2023

Status

approved