A182671 a(n) = the smallest n-digit number with exactly 6 divisors, a(n) = 0 if no such number exists.

0, 12, 116, 1004, 10012, 100017, 1000028, 10000036, 100000036, 1000000017, 10000000004, 100000000017, 1000000000028, 10000000000036, 100000000000019, 1000000000000025, 10000000000000091, 100000000000000028, 1000000000000000179, 10000000000000000196

Offset

1,2

Comments

a(n) = the smallest n-digit number of the form p^5 or p^2*q^1, (p, q = distinct primes), a(n) = 0 if no such number exists.

Links

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

Formula

A000005(a(n)) = 6.

Mathematica

Table[k=10^(n-1); While[k<10^n && DivisorSigma[0, k] != 6, k++]; If[k==10^n, k=0]; k, {n, 10}]

Crossrefs

Cf. A182672 (largest n-digit number with exactly 6 divisors).

Sequence in context: A027285 A238930 A304827 * A154346 A016142 A105218

Adjacent sequences: A182668 A182669 A182670 * A182672 A182673 A182674

Keyword

nonn,base

Author

Jaroslav Krizek, Nov 27 2010

Extensions

Extended by T. D. Noe, Nov 29 2010

Status

approved