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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:
4 Answers
- MichaelLv 41 decade agoFavorite 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
- Scythian1950Lv 71 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.
- Astral WalkerLv 71 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.
- elveraLv 45 years ago
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