A182685 a(n) = the smallest n-digit number with exactly 13 divisors, a(n) = 0 if no such number exists.

0, 0, 0, 4096, 0, 531441, 0, 0, 244140625, 0, 13841287201, 0, 3138428376721, 23298085122481, 582622237229761, 2213314919066161, 21914624432020321, 353814783205469041, 6582952005840035281, 22563490300366186081

Offset

1,4

Comments

a(n) = the smallest n-digit number of the form p^12 (p = prime), a(n) = 0 if no such number exists.

Links

Table of n, a(n) for n=1..20.

Formula

A000005(a(n)) = 13.

a(n) = A182686(n) for n <= 17.

Maple

A055642 := proc(n) max(1, ilog10(n)+1) ; end proc:
A182685 := proc(n) for i from 1 do p := ithprime(i)^12 ; if A055642(p) > n then return 0 ; elif A055642(p) = n then return p; end if; end do: end proc:

Crossrefs

Cf. A030631, A182686.

Sequence in context: A069439 A212935 A076154 * A182686 A369823 A176768

Adjacent sequences: A182682 A182683 A182684 * A182686 A182687 A182688

Keyword

nonn,base

Author

Jaroslav Krizek, Nov 27 2010

Status

approved