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Seeking the largest "Small Brain Number". Upper and/or lower bounds?

A small brain number is an "n" digit number equal to the sum of the n-th powers of its digits.

3-digit example: 153 = 1³ + 5³ + 3³

4-digit example: 8208 = 8^4 + 2^4 + 0^4 + 8^4

61 digits (or larger) is impossible since 61×(9^61) is only a 60-digit number.

Can we narrow down the gap?

This is a follow up to Riley's question:

http://answers.yahoo.com/question/index?qid=201102...

4 Answers

Relevance
  • 1 decade ago
    Favorite Answer

    Edit2:

    All calculations for nothing.

    Someone else did it before ^^

    XXX http://oeis.org/A005188 XXX

    115132219018763992565095597973971522401 , 39 digits.

    n=1 : 1,2,3,4,5,6,7,8,9

    n=3 : 153,370,371,407

    n=4 : 1634,8208,9474

    n=5 : 54748,92727,93084

    n=6 : 548834

    n=7 : 1741725,4210818,9800817,9926315

    n=8 : 24678050,24678051,88593477

    n=9 : 146511208,472335975,534494836,912985153

    n=10: 4679307774

    n=11: 32164049650,32164049651,

    40028394225,42678290603,

    44708635679,49388550606,

    82693916578,94204591914

    n=14: 28116440335967

    n=16: 4338281769391370,4338281769391371

    n=17: 21897142587612075,

    35641594208964132,

    35875699062250035

    n=19: 1517841543307505039,

    3289582984443187032,

    4498128791164624869,

    4929273885928088826

    n=20: 63105425988599693916

    n=21: 128468643043731391252,

    449177399146038697307

    n=23: 21887696841122916288858,

    27879694893054074471405,

    27907865009977052567814,

    28361281321319229463398,

    35452590104031691935943

    n=24: 174088005938065293023722,

    188451485447897896036875,

    239313664430041569350093

    n=25: 1550475334214501539088894,

    1553242162893771850669378,

    3706907995955475988644380,

    3706907995955475988644381,

    4422095118095899619457938

    n=27: 121204998563613372405438066,

    121270696006801314328439376,

    128851796696487777842012787,

    174650464499531377631639254,

    177265453171792792366489765

    n=29: 14607640612971980372614873089,

    19008174136254279995012734740,

    19008174136254279995012734741,

    23866716435523975980390369295

    n=31: 1145037275765491025924292050346,

    1927890457142960697580636236639,

    2309092682616190307509695338915

    n=32: 17333509997782249308725103962772

    @scythian: Do you have a prove that n=34 is an upper bound?

    I think I can cover 34 digits with a few hours of calculation.

    Edit: I upgraded my program and if i made no mistake n=50+ yields no results.

    n=33:

    186709961001538790100634132976990

    186709961001538790100634132976991

    n=34:

    1122763285329372541592822900204593

    So the maximum is either the one found for n=34 or one I didn't discover yet with n = 35..49

  • 1 decade ago

    I think the limit is a 34-digit number. How to even find the maximum seems like a fun problem.

    Edit: I now think the largest is much smaller than a 34-digit number, just from trying out a few numbers. The first few are as follows:

    153

    370

    371

    470

    1634

    8208

    9474

    54748

    92727

    93084

    548834

    1741725

    4210818

    9800817

    9926315

    24678050

    24678051

    More later.

    Edit 2: No, MIchael, I don't think 34-digits is the upper bound any more. My initial hunch was off.

  • 1 decade ago

    Is there any reason to limit these to numbers to base 10?

    For example, 1^2 + 4^2 = 14 in base 13 which is 17 in base 10.

    So you may or may not find a maximum for a particular base but I would imagine that there are an infinite number when expanded to any integer base b.

  • elvera
    Lv 4
    5 years ago

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