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A247264 Smallest positive number not divisible by 10 whose square remains a square when prefixed with 10^n. 4
15, 75, 11252109375, 375, 9694963627295445503856592180983186990852118469774723052978515625, 6841439843263141047421876154427540653587129781953990459442138671875 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..5.

EXAMPLE

a(0) = 15 since 15^2 = 225 and 1225 is square and 15 is the smallest number not ending in 0 with this property. a(3) = 375 since 375^2 = 140625 and 1000140625 is square and 375 is the smallest number not ending in 0 with this property.

PROG

(PARI)

a(n)=k=1; while(k^2%100==0||!issquare(10^(#Str(k^2)+n)+k^2), k++); k^2

n=0; while(n<10, print1(a(n), ", "); n++) \\ Derek Orr, Sep 13 2014

CROSSREFS

Cf. A242268, A247261, A247262, A247263, A247312.

Sequence in context: A007328 A222909 A049391 * A212093 A212241 A000477

Adjacent sequences:  A247261 A247262 A247263 * A247265 A247266 A247267

KEYWORD

nonn,base

AUTHOR

Chai Wah Wu, Sep 11 2014

STATUS

approved

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Last modified July 4 15:25 EDT 2020. Contains 335448 sequences. (Running on oeis4.)