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A175345 Numbers n such that A006218(n) is a perfect square. 2
1, 7, 101, 312, 351, 448, 479, 726, 781, 897, 1040, 1580, 1605, 2159, 2339, 2783, 3298, 3739, 4485, 4608, 4650, 4735, 4776, 4902, 5473, 6746, 6894, 6994, 8353, 8961, 10117, 10658, 11714, 12226, 13758, 14309, 14729, 15512, 18446, 18682 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..286

EXAMPLE

If A027750 is displayed as a triangle where the row lengths are successive odd integers:

              1;   <-- 1

           1, 2; 1,

        3; 1, 2, 4; 1,

     5; 1, 2, 3, 6; 1, 7:  <-- 7

  1, 2, 4, 8; 1, 3, 9; 1, 2,

...

MAPLE

N:= 10^5: # to get all entries up to N

A:= Vector(N, numtheory:-tau, datatype=integer[8]):

C:= Statistics:-CumulativeSum(A);

select(t -> issqr(round(C[t])), [$1..N]); # Robert Israel, May 19 2014

PROG

(PARI) lista(nn) = {s = 0; for (n=1, nn, s += numdiv(n); if (issquare(s), print1(n, ", ")); ); } \\ Michel Marcus, Oct 19 2015

CROSSREFS

Cf. A000005, A006218, A027750.

Sequence in context: A182529 A322909 A165878 * A142358 A210684 A329239

Adjacent sequences:  A175342 A175343 A175344 * A175346 A175347 A175348

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka, Apr 17 2010

STATUS

approved

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Last modified September 22 00:42 EDT 2020. Contains 337276 sequences. (Running on oeis4.)