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A060376 If 10^n can be written as x*y where the digits of x and y are all nonzero, then let a(n) = smallest such x, otherwise a(n) = -1. 1
1, 2, 4, 8, 16, 32, 64, 128, -1, 512, -1, -1, -1, -1, -1, -1, -1, -1, 262144, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 8589934592, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

According to Ogilvy and Anderson, 10^33 is the highest known power of ten that can be expressed as the product of two zero-free factors. "If there is another one, it is greater than 10^5000." p. 89

REFERENCES

C. Stanley Ogilvy and John T. Anderson, Excursions in Number Theory, Oxford University Press, 1966, p. 89.

Rudolph Ondrejka, Nonzero factors of 10^n, Recreational Mathematics Magazine, no. 6 (1961), p. 59.

LINKS

Table of n, a(n) for n=0..79.

EXAMPLE

10^2 = 4 * 25, so a(2) = 4.

CROSSREFS

Cf. A060391 (for values of y).

Sequence in context: A251761 A133024 A243085 * A047869 A270201 A016025

Adjacent sequences:  A060373 A060374 A060375 * A060377 A060378 A060379

KEYWORD

sign,base

AUTHOR

Jason Earls, Apr 02 2001

STATUS

approved

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Last modified December 8 07:37 EST 2021. Contains 349593 sequences. (Running on oeis4.)