A182677 a(n) = the smallest n-digit number with exactly 9 divisors, a(n) = 0 if no such number exists.

0, 36, 100, 1089, 11236, 101761, 1006009, 10023556, 100020001, 1000520161, 10000200001, 100000780441, 1000002000001, 10000021122961, 100000020000001, 1000000341419524, 10000000200000001, 100000004416539529, 1000000012000000036, 10000000017908741569, 100000000060000000009, 1000000000083244219609, 10000000001400000000049, 100000000002632322172441, 1000000000014000000000049

Offset

1,2

Comments

a(n) = the smallest n-digit number of the form p^8 or p^2*q^2 (p, q = distinct primes), a(n) = 0 if no such number exists.

Links

Table of n, a(n) for n=1..25.

Formula

A000005(a(n)) = 9.

Mathematica

Table[k=10^(n-1); While[k<10^n && DivisorSigma[0, k] != 9, k++];  If[k==10^n, k=0]; k, {n, 20}]

Crossrefs

See A182678(n) - the largest n-digit number with exactly 9 divisors.

Sequence in context: A323064 A163246 A014738 * A076768 A282853 A341046

Adjacent sequences: A182674 A182675 A182676 * A182678 A182679 A182680

Keyword

nonn,base

Author

Jaroslav Krizek, Nov 27 2010

Extensions

Extended by T. D. Noe, Nov 29 2010

a(11)-a(25) from Robert Gerbicz, Nov 29 2010

Status

approved