login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A166721 Squares for which no smaller square has the same number of divisors. 2
1, 4, 16, 36, 64, 144, 576, 900, 1024, 1296, 3600, 4096, 5184, 9216, 14400, 32400, 36864, 44100, 46656, 65536, 82944, 129600, 176400, 230400, 262144, 331776, 589824, 705600, 746496, 810000, 921600, 1166400, 1587600, 2073600, 2359296, 2822400, 2985984, 3240000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

From Jon E. Schoenfield, Mar 03 2018: (Start)

Numbers k^2 such there is no positive m < k such that A000005(m^2) = A000005(k^2).

Square terms in A007416. (End)

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..300

EXAMPLE

The positive squares begin 1, 4, 9, 16, 25, 36, 49, 64, ..., and their corresponding numbers of divisors are 1, 3, 3, 5, 3, 9, 3, 7, ...; thus, a(1)=1, a(2)=4, 9 is not a term (it has the same number of divisors as does 4; the same is true of 25, 49, etc.), a(3)=16, a(4)=36, a(5)=64, ... - Jon E. Schoenfield, Mar 03 2018

PROG

(PARI) lista(nn) = {v = []; for (n=1, nn, d = numdiv(n^2); if (! vecsearch(v, d), print1(n^2, ", "); v = Set(concat(v, d))); ); } \\ Michel Marcus, Mar 04 2018

CROSSREFS

Cf. A000005, A005179, A007416, A048691, A136404, A166722.

Sequence in context: A121317 A238259 A063755 * A085040 A030179 A207025

Adjacent sequences:  A166718 A166719 A166720 * A166722 A166723 A166724

KEYWORD

easy,nonn

AUTHOR

Alexander Isaev (i2357(AT)mail.ru), Oct 20 2009

EXTENSIONS

Proper definition and substantial editing by Jon E. Schoenfield, Mar 03 2018

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 18 19:32 EST 2020. Contains 331029 sequences. (Running on oeis4.)