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A097251 Numbers whose set of base 5 digits is {0,4}. 13
0, 4, 20, 24, 100, 104, 120, 124, 500, 504, 520, 524, 600, 604, 620, 624, 2500, 2504, 2520, 2524, 2600, 2604, 2620, 2624, 3000, 3004, 3020, 3024, 3100, 3104, 3120, 3124, 12500, 12504, 12520, 12524, 12600, 12604, 12620, 12624, 13000, 13004, 13020 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

n such that there exists a permutation p_1, ..., p_n of 1, ..., n such that i + p_i is a power of 5 for every i.

The first 2^n terms of the sequence could be obtained using the Cantor-like process for the segment [0,5^n-1]. For example, for n=1 we have [0, {1,2,3},4] such that numbers outside of braces are the first 2 terms of the sequence; for n=2 we have [0, {1,2,3}, 4, {5,...,19}, 20, {21,22,23}, 24] such that the numbers outside of braces are the first 4 terms of the sequence, etc. - Vladimir Shevelev, Dec 17 2012

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = 4*A033042(n).

a(2n) = 5*a(n), a(2n+1) = a(2n)+4.

MATHEMATICA

fQ[n_]:=Union@Join[{0, 4}, IntegerDigits[n, 5]]=={0, 4}; Select[Range[0, 20000], fQ] (* Vincenzo Librandi, May 25 2012 *)

FromDigits[#, 5]&/@Tuples[{0, 4}, 6] (* Harvey P. Dale, Feb 01 2015 *)

PROG

(MAGMA) [n: n in [0..20000] | Set(IntegerToSequence(n, 5)) subset {0, 4}]; // Vincenzo Librandi, May 25 2012

(Maxima) a[0]:0$ a[n]:=5*a[floor(n/2)]+2*(1-(-1)^n)$ makelist(a[n], n, 0, 42); [Bruno Berselli, May 25 2012]

CROSSREFS

Cf. A001196, A005823, A097252-A097262.

Sequence in context: A174134 A032425 A194045 * A202070 A198831 A259755

Adjacent sequences:  A097248 A097249 A097250 * A097252 A097253 A097254

KEYWORD

nonn,base

AUTHOR

Ray Chandler, Aug 03 2004

STATUS

approved

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Last modified August 20 11:41 EDT 2017. Contains 290835 sequences.