A247264 Smallest positive number not divisible by 10 whose square remains a square when prefixed with 10^n.

15, 75, 11252109375, 375, 9694963627295445503856592180983186990852118469774723052978515625, 6841439843263141047421876154427540653587129781953990459442138671875

Offset: 0

Author

Chai Wah Wu, Sep 11 2014

Keywords

• nonn
• base

Examples

			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.
		

Crossrefs

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

Programs

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