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A099542 Rhonda numbers to base 10. 21
1568, 2835, 4752, 5265, 5439, 5664, 5824, 5832, 8526, 12985, 15625, 15698, 19435, 25284, 25662, 33475, 34935, 35581, 45951, 47265, 47594, 52374, 53176, 53742, 54479, 55272, 56356, 56718, 95232, 118465, 133857, 148653, 154462, 161785 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

An integer n is a Rhonda number to base b if the product of its digits in base b equals b*Sum of prime factors of n (including multiplicity).

Does every Rhonda number to base 10 contain at least one 5? [From Howard Berman (howard_berman(AT)hotmail.com), Oct 22 2008]

Yes, every Rhonda number m to base 10 contains at least one 5 and also one even digit, otherwise A007954(m) mod 10 > 0. - Reinhard Zumkeller, Dec 01 2012

A007954(a(n)) = 10 * A001414(a(n)).

LINKS

Harvey P. Dale and Reinhard Zumkeller, Table of n, a(n) for n = 1..1000, first 180 terms by Harvey P. Dale.

Kevin Brown, Infinitely Many Rhondas.

Walter Schneider, Rhonda Numbers

Eric Weisstein's World of Mathematics, Rhonda Number

Giovanni Resta, Rhonda numbers the 64507 base-10 Rhonda numbers up to 10^12

EXAMPLE

1568 has prime factorization 2^{5} 7^{2}. Sum of prime factors=2*5+7*2=24. Product of digits of 1568=1*5*6*8=240 = 10*24, hence 1568 is a Rhonda number to base 10.

MATHEMATICA

Select[Range[200000], 10Total[Times@@@FactorInteger[#]]==Times@@ IntegerDigits[ #]&] (* Harvey P. Dale, Oct 16 2011 *)

PROG

(Haskell)

import Data.List (unfoldr); import Data.Tuple (swap)

a099542 n = a099542_list !! (n-1)

a099542_list = filter (rhonda 10) [1..]

rhonda b x = a001414 x * b == product (unfoldr

       (\z -> if z == 0 then Nothing else Just $ swap $ divMod z b) x)

-- Reinhard Zumkeller, Mar 05 2015, Dec 01 2012

CROSSREFS

Cf. Rhonda numbers to other bases: A100968 (base 4), A100969 (base 6), A100970 (base 8), A100973 (base 9), A100971 (base 12), A100972 (base 14), A100974 (base 15), A100975 (base 16), A255735 (base 18), A255732 (base 20), A255736 (base 30), A255731 (base 60), see also A255880.

Cf. A001414, A027746, A007954.

Column k=5 of A291925.

Sequence in context: A035890 A252109 A045276 * A232672 A232036 A035765

Adjacent sequences:  A099539 A099540 A099541 * A099543 A099544 A099545

KEYWORD

base,nice,nonn

AUTHOR

Mark Hudson (mrmarkhudson(AT)hotmail.com), Oct 21 2004

STATUS

approved

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Last modified November 18 09:07 EST 2017. Contains 294873 sequences.