A175345 Numbers m such that A006218(m) is a perfect square.

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

Offset

1,2

Links

Chai Wah Wu, Table of n, a(n) for n = 1..10000 (terms 1..286 from Robert Israel)

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
(Python)
from sympy import integer_nthroot, divisor_count
A175345_list, k, c, = [], 1, 1
while k < 10**4:
    if integer_nthroot(c, 2)[1]: A175345_list.append(k)
    k += 1
    c += divisor_count(k) # Chai Wah Wu, Oct 11 2021

Crossrefs

Cf. A000005, A006218, A027750.

Sequence in context: A182529 A322909 A165878 * A142358 A210684 A367137

Adjacent sequences: A175342 A175343 A175344 * A175346 A175347 A175348

Keyword

easy,nonn

Author

Ctibor O. Zizka, Apr 17 2010

Status

approved