login
This site is supported by donations to The OEIS Foundation.

 

Logo

Many excellent designs for a new banner were submitted. We will use the best of them in rotation.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A032799 Numbers n such that n equals the sum of its digits raised to the consecutive powers (1,2,3,...). 8
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 89, 135, 175, 518, 598, 1306, 1676, 2427, 2646798, 12157692622039623539 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Lemma: The sequence is finite with all terms in the sequence having at most 22 digits. Proof: Let n be an m-digit natural number in the sequence for some m. Then 10^(m-1)<=n and n<=9+9^2+...9^m = 9(9^m-1)/8<(9^(m+1))/8. Thus 10^(m-1)<(9^(m+1))/8. Taking logarithms of both sides and solving yields m<22.97 QED. Note proof is identical to that for A208130. [Francis J. McDonnell, Apr 14 2012]

REFERENCES

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 175, p. 55, Ellipses, Paris 2008.

Ken Follett, Code to Zero, Dutton, a Penguin Group, NY 2000, p. 84.

D. Wells, The Penguin Dictionary of Curious and Interesting Numbers, Penguin Books, London, 1986, Entry 175.

LINKS

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

Eric Weisstein's World of Mathematics, Narcissistic Number

EXAMPLE

89 = 8^1 + 9^2.

175 = 1^1 + 7^2 + 5^3.

2427 = 2^1 + 4^2 + 2^3 + 7^4.

2646798 = 2^1 + 6^2 + 4^3 + 6^4 + 7^5 + 9^6 + 8^7.

MATHEMATICA

f[n_] := Plus @@ (IntegerDigits[n]^Range[ Floor[ Log[10, n] + 1]]); Select[ Range[10^7], f[ # ] == # &] (* from Robert G. Wilson v, May 04 2005 *)

CROSSREFS

Sequence in context: A135480 A228326 A098766 * A208130 A160343 A239085

Adjacent sequences:  A032796 A032797 A032798 * A032800 A032801 A032802

KEYWORD

nonn,base,fini,full,nice

AUTHOR

Patrick De Geest, May 15, 1998.

EXTENSIONS

Corrected by Macsy Zhang (macsy(AT)21cn.com), Feb 17, 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified April 24 18:58 EDT 2014. Contains 240988 sequences.