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A323784 Prime numbers such that the reverse of the balanced ternary representation is neither prime nor a negated prime. 1
3, 19, 23, 41, 47, 67, 79, 97, 107, 109, 113, 127, 131, 151, 157, 167, 191, 197, 211, 227, 229, 239, 251, 257, 271, 281, 283, 293, 307, 317, 337, 349, 359, 397, 409, 419, 431, 433, 439, 461, 463, 491, 503, 521, 523, 557, 563, 571, 577, 587, 593, 617, 619, 631, 641, 647, 653, 659, 661, 673, 683, 701, 733, 743, 769, 787, 797 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..67.

Github, Python code repository

Rosetta Code, Balanced Ternary Code

Wikipedia, Balanced Ternary

EXAMPLE

79 is a term:

79 is +00-+ in balanced ternary notation

+00-+ reversed is +-00+

+-00+ is 55 in balanced ternary notation

55 prime factors are 5 and 11

Therefore 55 is not prime.

Therefore the prime number 79 "warps" to the nonprime number 55.

This operation is reversible: 55 "warps" to 79.

PROG

(Python) See links

(PARI) d3(n) = if ((n%3)==2, n\3+1, n\3);

m3(n) = if ((n%3)==2, -1, n % 3);

t(n) = if (n==0, [0], if (abs(n) == 1, [n], concat(m3(n), t(d3(n)))));

f(n) = subst(Pol(Vec(t(n))), x, 3);

isok(n) = isprime(n) && !isprime(abs(f(n))); \\ Michel Marcus, Jan 29 2019

CROSSREFS

Cf. A134028, A323782.

Complement of A323782 among primes.

Sequence in context: A191074 A019408 A070045 * A063557 A197541 A273367

Adjacent sequences:  A323781 A323782 A323783 * A323786 A323787 A323788

KEYWORD

nonn,base

AUTHOR

Philippe Cochin, Jan 28 2019

STATUS

approved

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Last modified October 15 13:06 EDT 2019. Contains 328030 sequences. (Running on oeis4.)