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A087331 Smallest number with all identical digits having n distinct prime divisors. 3
1, 2, 6, 66, 6666, 111111, 222222, 111111111111, 222222222222, 222222222222222222, 111111111111111111111111, 222222222222222222222222, 22222222222222222222222222222222, 111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The conjecture that 'for n > 2, a(n) == 0 (mod 3)' is not true since a(12) = 32 2's which is == 1 (mod 3). - Robert G. Wilson v

Sequence could be represented by citing the number of repeated digits concatenated with that digit, e.g., a(8) = 122. See A087450.

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

a(6) = 22222222 because the 6 distinct prime divisors of a(6) are 2, 3, 7, 11, 13, and 37.

MATHEMATICA

PrimeFactors[n_Integer] := Flatten[ Table[ # [[1]], {1}] & /@ FactorInteger[n]]; Do[k = 1; While[t = Table[j*(10^k - 1)/9, {j, 1, 9}]; l = Map[ Length, Map[ PrimeFactors, t]]; Position[l, n] == {}, k++ ]; Print[ t[[Position[l, n] [[1, 1]]]]], {n, 0, 13}]

CROSSREFS

Sequence in context: A091458 A335934 A167006 * A097419 A219037 A156458

Adjacent sequences:  A087328 A087329 A087330 * A087332 A087333 A087334

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Sep 05 2003

EXTENSIONS

Edited, corrected and extended by Robert G. Wilson v, Sep 06 2003

STATUS

approved

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Last modified October 22 01:46 EDT 2020. Contains 337948 sequences. (Running on oeis4.)