The OEIS is supported by the many generous donors to the OEIS Foundation.

A354530
Numbers k such that k^2 is a minimal number; numbers k whose square is in A007416.
1
1, 2, 4, 6, 8, 12, 24, 30, 32, 36, 60, 64, 72, 96, 120, 180, 192, 210, 216, 256, 288, 360, 420, 480, 512, 576, 768, 840, 864, 900, 960, 1080, 1260, 1440, 1536, 1680, 1728, 1800, 2048, 2304, 2520, 2880, 3360, 3840, 4320, 4608, 4620, 5400, 6144, 6300, 6720, 6912, 7200, 7560
OFFSET
1,2
Numbers k such that there is no m < k^2 such that d(m) = d(k^2), d = A000005. Since only squares have an odd number of divisors, also numbers k such that there is no m < k such that d(m^2) = d(k^2).
David A. Corneth, Table of n, a(n) for n = 1..14008 (first 310 terms from Jianing Song, terms <= 10^20).
FORMULA
d(a(n)^2) = A166722(n).
EXAMPLE
8 is a term since 8^2 = 64 has 7 divisors and no smaller number (smaller square) has that many divisors.
PROG
(PARI) lista(nn) = {v = []; for (n=1, nn, d = numdiv(n^2); if (! vecsearch(v, d), print1(n, ", "); v = Set(concat(v, d))); ); } \\ from Michel Marcus's program for A166721
CROSSREFS
Square root of A166721. Also A016017 or A071571 sorted.
Cf. also A166722.
Sequence in context: A228515 A363145 A164145 * A140999 A168267 A308912
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Aug 16 2022
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 19 21:59 EDT 2024. Contains 376015 sequences. (Running on oeis4.)