A357515 Smallest positive integer that doubles when the n rightmost digits are shifted to the left end.

105263157894736842, 100502512562814070351758793969849246231155778894472361809045226130653266331658291457286432160804020

Offset

1,1

Comments

a(n) with n>=3 is too large to be written in data.

The following is a method for finding a(n): Let n be the number of digits shifted, and let m be the smallest positive integer such that 10^m = 2 mod 2*10^n-1. We then look for the smallest positive b that is an n+d digit number and satisfies b = c(10^n-2)/(2*10^d-1), where c is a positive integer. Then a(n) = c(10^n-2)/(2*10^d-1)*10^n+c.

Links

Table of n, a(n) for n=1..2.

Example

a(1) = 105263157894736842 because shifting the 1 rightmost digit to the left end gives 210526315789473684 which is double a(1).

Crossrefs

Cf. A146088

Sequence in context: A092697 A097717 A128857 * A246111 A067818 A262560

Adjacent sequences: A357512 A357513 A357514 * A357516 A357517 A357518

Keyword

nonn,base

Author

Joseph C. Y. Wong, Oct 01 2022

Status

approved