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A182678 a(n) = the largest n-digit number with exactly 9 divisors, a(n) = 0 if no such number exists. 1
0, 36, 676, 9025, 98596, 996004, 9991921, 99960004, 999887641, 9999600004, 99998883076, 999994000009, 9999970526529, 99999960000004, 999999645718441, 9999999400000009, 99999998091984169, 999999982000000081, 9999999904066746025, 99999999940000000009, 999999999956753113201, 9999999999400000000009, 99999999997572677916169, 999999999994000000000009, 9999999999940679895905281 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = the largest 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-1) && DivisorSigma[0, k] != 9, k--]; If[k==10^(n-1), k=0]; k, {n, 10}]

CROSSREFS

Cf. A182677 (smallest n-digit number with exactly 9 divisors).

Sequence in context: A010988 A000815 A271794 * A239181 A053947 A157092

Adjacent sequences:  A182675 A182676 A182677 * A182679 A182680 A182681

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

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Last modified September 25 10:45 EDT 2022. Contains 356978 sequences. (Running on oeis4.)