

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
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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



