OFFSET
1,1
COMMENTS
The sum of reciprocals, Sum_{n>=1} 1/a(n), converges. In general, the sum of the reciprocals of balanced numbers in base b converges for all b >= 4, and diverges for b = 2 or 3 (Papanicolaou, 2013). Grivaux (2015) gives 3 * Sum_{k>=1} (4*k)!/(k!^4 * 4^(4*k)) = 0.857... as an upper bound for this sum. The sum is converging slowly: the sums of the reciprocals of the terms with no more than 4*k digits in base 4, for k = 1, 2, ..., are 0.129.., 0.183..., 0.213..., 0.233..., 0.248..., 0.260..., 0.269..., 0.276..., 0.282..., 0.288..., ... . - Amiram Eldar, Feb 15 2024
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1001
Vassilis Papanicolaou, Problem 11729, The American Mathematical Monthly, Vol. 120, No. 8 (2013), p. 754; Summing the Reciprocals of Normal Numbers Base b, Solution to Problem 11729 by Nicole Grivaux, ibid., Vol. 122, No. 8 (2015), p. 806.
Roberto Tauraso, Problem 11729.
MATHEMATICA
Select[Range[20000], Length[Union[DigitCount[#, 4]]]==1&] (* Harvey P. Dale, Mar 19 2013 *)
FromDigits[#, 4]&/@DeleteCases[Flatten[Permutations/@Table[PadRight[{}, 4n, {1, 0, 2, 3}], {n, 2}], 1], _?(#[[1]]==0&)]//Sort (* Harvey P. Dale, May 30 2016 *)
PROG
(PARI) is(n) = {my(c = matreduce(digits(n, 4))[, 2]); #c == 4 && #Set(c) == 1; } \\ Amiram Eldar, Feb 15 2024
CROSSREFS
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
Offset corrected by Amiram Eldar, Feb 15 2024
STATUS
approved