OFFSET

1,2

COMMENTS

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).

LINKS

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

KEYWORD

nonn,easy

AUTHOR

Jianing Song, Aug 16 2022

STATUS

approved