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A104264 Number of n-digit squares with no zero digits. 11
3, 6, 19, 44, 136, 376, 1061, 2985, 8431, 24009, 67983, 193359, 549697, 1563545, 4446173, 12650545, 35999714, 102439796, 291532841, 829634988, 2360947327, 6719171580, 19122499510, 54423038535, 154888366195 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Comments from David W. Wilson, Feb 26 2005: (Start)

"There are approximately s(d) = (10^d)^(1/2) - (10^(d-1))^(1/2) d-digit squares. A random d-digit number has the probability p(d) = (9/10)^(d-1) of being zeroless (exponent d-1 as opposed to d because the first digit is not zero). So we expect p(d)s(d) zeroless d-digit squares.

"For d = 1 through 12, we get (truncating): 1, 5, 15, 44, 127, 363, 1034, 2943, 8377, 23841, 67854, 193117, ... The elements grow approximately geometrically with limit ratio (9/10)*10^(1/2) = 2.846+.

"The same naive estimate can easily be generalize to k-th powers, giving the estimate s(d) = (10^d)^(1/k) - (10^(d-1))^(1/k) for d-digit k-th powers. p(d) remains the same. The resulting estimates have ratio (9/10)*10^(1/k).

"We should expect an infinite number of zeroless k-th powers when this ratio is >= 1, which it is for k <= 21. For k >= 22, the ratio is < 1 and we should expect a finite number of zeroless k-th powers." (End)

LINKS

Table of n, a(n) for n=1..25.

EXAMPLE

a(3) = #{121, 144, 169, 196, 225, 256, 289, 324, 361, 441, 484, 529, 576, 625, 676, 729, 784, 841, 961} = 19.

PROG

(Python)

def aupton(terms):

  c, k, kk = [0 for i in range(terms)], 1, 1

  while kk < 10**terms:

    s = str(kk)

    c[len(s)-1], k, kk = c[len(s)-1] + (s.count('0')==0), k+1, kk + 2*k + 1

  return c

print(aupton(14)) # Michael S. Branicky, Mar 06 2021

CROSSREFS

Cf. A052041, A104265, A104266, A075415, A102807.

Sequence in context: A203797 A019097 A219286 * A007098 A226322 A148566

Adjacent sequences:  A104261 A104262 A104263 * A104265 A104266 A104267

KEYWORD

nonn,base,more

AUTHOR

Reinhard Zumkeller and Ron Knott, Feb 26 2005

EXTENSIONS

a(14)-a(18) from Donovan Johnson, Nov 05 2009

a(19)-a(21) from Donovan Johnson, Mar 23 2011

a(22)-a(25) from Donovan Johnson, Jan 29 2013

STATUS

approved

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Last modified July 25 11:26 EDT 2021. Contains 346289 sequences. (Running on oeis4.)