

A261433


kdigit integers equal to the sum of the kth powers of the tens' complements of their digits.


3




OFFSET

1,1


COMMENTS

The terms of the sequence could be called "Shy n ndigit numbers" as suggested by Geoffrey Campbell, Long Term Visitor (Visiting Fellow), Mathematical Sciences Institute, Australian National University, cf Links.
In base 10, x is a "Shy k ndigit number" if it is an ndigit (d_i) number such that x = Sum_{i=1..n}{(10d_i)^k}. For instance, 2240 is a "Shy 3 4digit number": (10  2)^3 + (10  2)^3 + (10  4)^3 + (10  0)^3 = 512 + 512 + 216 + 1000 = 2240. Again, 2149042 is a "Shy 6 7digit number": (10  2)^6 + (10  1)^6 + (10  4)^6 + (10  9)^6 + (10  0)^6 + (10  4)^6 + (10  2)^6 = 262144 + 531441 + 46656 + 1 + 1000000 + 46656 + 262144 = 2149042.
It is not known if the sequence is finite. At least there are no other terms up to 18digit numbers (as tested by Marco Cecchi at LinkedIn link).
If there are further terms, they are greater than 10^33.  Giovanni Resta, Aug 20 2015
Subsequence of A052382. Sequence is finite and complete as verified by exhaustive search since all terms have 60 or fewer digits. Since all terms are zeroless, they are less than k*9^k which would be less than 10^(k1) (i.e., have fewer than k digits) if k > 60.  Chai Wah Wu, Apr 07 2018


LINKS

Table of n, a(n) for n=1..6.
Geoffrey Campbell, Related to Narcissistic numbers: the Shy numbers, Number Theory group on LinkedIn.com
Marco Cecchi, Python program based on partitions.


EXAMPLE

(10  5)^1 = 5,
(10  3)^3 + (10  7)^3 + (10  8)^3 = 343 + 27 + 8 = 378,
(10  9)^5 + (10  1)^5 + (10  8)^5 + (10  8)^5 + (10  2)^5 = 1 + 59049 + 32 + 32 + 32768 = 91882, etc.


MAPLE

with(numtheory): P:=proc(q) local a, b, c, k, n;
for n from 1 to q do a:=ilog10(n)+1; b:=0; c:=n;
for k from 1 to a do b:=b+(10(c mod 10))^a; c:=trunc(c/10); od;
if b=n then print(n); fi; od; end: P(10^9);


MATHEMATICA

Select[Range[10^5], # == Total[(10  IntegerDigits@ #)^ IntegerLength[#]] &] (* Giovanni Resta, Aug 20 2015 *)


PROG

(PARI) isok(n) = (d = digits(n)) && (sum(k=1, #d, (10d[k])^#d) == n); \\ Michel Marcus, Aug 24 2015
(Python)
from itertools import combinations_with_replacement
A261433_list = []
for k in range(1, 10):
a, k10 = tuple([i**k for i in range(10, 0, 1)]), 10**k
for b in combinations_with_replacement(range(1, 10), k):
x = sum(list(map(lambda y:a[y], b)))
if x < k10 and tuple(int(d) for d in sorted(str(x))) == b:
A261433_list.append(x)
A261433_list = sorted(A261433_list) # Chai Wah Wu, Aug 25 2015, updated Apr 06, 2018


CROSSREFS

Cf. A005188, A052382.
Sequence in context: A214008 A208094 A273397 * A206386 A198902 A100474
Adjacent sequences: A261430 A261431 A261432 * A261434 A261435 A261436


KEYWORD

nonn,base,fini,full


AUTHOR

Paolo P. Lava, Aug 20 2015


EXTENSIONS

a(4)a(6) found by Aleksander Zujev


STATUS

approved



