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A276982 a(n) = number of primes p whose balanced ternary representation is compatible with the binary representation of A276194(n). 1
4, 6, 8, 10, 10, 10, 7, 19, 18, 16, 19, 17, 16, 11, 20, 19, 21, 22, 21, 19, 30, 21, 22, 23, 30, 22, 30, 30, 30, 7, 24, 27, 23, 28, 24, 29, 45, 25, 29, 20, 53, 28, 50, 45, 50, 30, 24, 25, 48, 25, 45, 40, 45, 26, 53, 48, 53, 45, 50, 45, 10, 27, 26, 32, 24, 26 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Let B = binary representation of A276194(n), and let C = C(p) = balanced ternary (bt) representation of a prime p (see A117966). Thus C is a string of 0's, 1's, and -1's. We will write T instead of -1.

We say that C is compatible with B if (i) length(C) = length(B); (ii) C has a 1 or T wherever B has a 1; and (iii) there is exactly one 1 or T in C in the positions where B is 0, and otherwise C has a 0 whenever B has a 0.

Then a(n) is the number of primes p for which C(p) is compatible with B.

It is conjectured that all a(n) > 0.  This has been checked for n <= 100000. But it is possible that there is a counterexample for very large n.

LINKS

Lei Zhou, Table of n, a(n) for n = 1..10000

EXAMPLE

n=1, A276194(1) = 5, or 101 in binary form. Using this as mask to generate positive balanced ternary numbers that allow 1 or T on all 1 digits, but only one digits 1 or T falls on a 0 digits, the following balanced ternary numbers can be generated: 1TT=5, 1T1=7, 11T=11, 111=13. All the four numbers are primes.  So a(1)=4.

n=2, A276194(2) = 9, or 1001 in binary form. Using this as mask to generate positive balanced ternary numbers that allow 1 or T on all 1 digits, but only one digits 1 or T falls on a 0 digits, the following balanced ternary numbers can be generated: 1T0T=17, 1T01=19, 10TT=23, 10T1=25, 101T=29, 1011=31, 110T=35, 1101=37.  Among the 8 numbers, 6 of them (17, 19, 23, 29, 31, and 37) are primes.  So a(2)=6.

MATHEMATICA

BNDigits[m_Integer] := Module[{n = m, d, t = {}},

   While[n > 0, d = Mod[n, 2]; PrependTo[t, d]; n = (n - d)/2]; t];

c = 1;

Table[ While[c = c + 2; d = BNDigits[c]; ld = Length[d];

   c1 = Total[d]; !(EvenQ[c1] && (c1 < ld))];

  l = Length[d]; flps = Flatten[Position[Reverse[d], 1]] - 1;

  flps = Delete[flps, Length[flps]];

  sfts = Flatten[Position[Reverse[d], 0]] - 1; lf = Length[flps]; ls = Length[sfts]; ct = 0;

  Do[Do[cp10 = 3^(l - 1) + 3^(sfts[[i]]);

    cp20 = 3^(l - 1) - 3^(sfts[[i]]); di = BNDigits[j];

    While[Length[di] < lf, PrependTo[di, 0]]; Do[

     If[di[[k]] == 0, cp10 = cp10 - 3^flps[[k]];

      cp20 = cp20 - 3^flps[[k]], cp10 = cp10 + 3^flps[[k]];

      cp20 = cp20 + 3^flps[[k]]], {k, 1, lf}];

    If[PrimeQ[cp10], ct++]; If[PrimeQ[cp20], ct++], {j, 0, 2^lf - 1}], {i, 1, ls}]; ct, {n, 1, 66}]

CROSSREFS

Cf. A276194.

Sequence in context: A145256 A087789 A071830 * A340846 A167146 A020891

Adjacent sequences:  A276979 A276980 A276981 * A276983 A276984 A276985

KEYWORD

nonn,base

AUTHOR

Lei Zhou, Oct 20 2016

EXTENSIONS

Edited by N. J. A. Sloane, Nov 05 2016

STATUS

approved

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Last modified May 6 17:59 EDT 2021. Contains 343586 sequences. (Running on oeis4.)