A204232 Numbers whose binary reversal is prime.
3, 5, 6, 7, 10, 11, 12, 13, 14, 17, 20, 22, 23, 24, 25, 26, 28, 29, 31, 34, 37, 40, 41, 43, 44, 46, 47, 48, 50, 52, 53, 55, 56, 58, 61, 62, 67, 68, 71, 73, 74, 77, 80, 82, 83, 86, 88, 91, 92, 94, 96, 97, 100, 101, 104, 106, 107, 110, 112, 113, 115, 116, 121
Offset: 1
Examples
3, 5 and 7 are in the sequence because their binary reversal, equal to themselves, is prime. a(3)=6 is in the sequence, because 6=110[2] (written in base 2), whose reversal 011[2]=3 is prime. a(5)=11 is in the sequence, because 11=1011[2] (written in base 2), whose reversal 1101[2]=13 is prime.
Links
- Michel Marcus, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
Select[Range[170], PrimeQ[FromDigits[Reverse[IntegerDigits[#, 2]], 2]] &] (* Alonso del Arte, Jan 13 2012 *)
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PARI
for(n=1,1e2,isprime((t=binary(n))*vector(#t,i,1<
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Python
from sympy import isprime def ok(n): return isprime(int(bin(n)[2:][::-1], 2)) print(list(filter(ok, range(1, 122)))) # Michael S. Branicky, Sep 06 2021
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Python
# alternate program constructing terms directly from primes from sympy import isprime, primerange def auptobits(maxbits): alst = [] for p in primerange(3, 1<
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