cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A272478 Primes with a prime number of binary digits, and with a prime number of 1's and a prime number of 0's.

Original entry on oeis.org

17, 19, 79, 103, 107, 109, 5119, 6079, 6911, 7039, 7103, 7151, 7159, 7919, 7927, 7933, 8059, 8111, 8123, 8167, 8171, 8179, 442367, 458239, 458719, 458747, 487423, 491503, 499711, 507839, 507901, 515839, 516091, 520063, 523007, 523261, 523519, 523759, 523771, 523903, 524219, 524221, 524269
Offset: 1

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Author

Andres Cicuttin, May 01 2016

Keywords

Comments

If the sum of primes p and q is a prime r, then one of p and q must be 2. - N. J. A. Sloane, May 01 2016

Examples

			a(3) = 79, its binary representation is 1001111 with (prime) 7 digits, (prime) 5 1's and (prime) 2 0's.
		

Crossrefs

Cf. A006512 (bitlengths of terms).

Programs

  • Mathematica
    Select[Table[Prime[j],{j,1,120000}],PrimeQ[Total@IntegerDigits[#,2]]&&PrimeQ[Length@IntegerDigits[#,2]]&&PrimeQ[(Length@IntegerDigits[#,2]-Total@IntegerDigits[#,2])]&]
    Select[Prime@ Range[10^5], And[PrimeQ@ Total@ #, PrimeQ@ First@ #, PrimeQ@ Last@ #] &@ DigitCount[#, 2] &] (* Michael De Vlieger, May 01 2016 *)
  • PARI
    isok(n) = isprime(n) && isprime(#binary(n)) && isprime(hammingweight(n)) && isprime(#binary(n) - hammingweight(n)); \\ Michel Marcus, May 01 2016
    
  • Python
    from sympy import isprime, nextprime
    from itertools import combinations, islice
    def agen(): # generator of terms
        p = 2
        while True:
            p = nextprime(p)
            if not isprime(p+2): continue
            if isprime(t:=(1<<(p+1))+1): yield t
            b = (1<<(p+2))-1
            for i, j in combinations(range(p), 2):
                if isprime(t:=b-(1<<(p-i))-(1<<(p-j))):
                    yield t
    print(list(islice(agen(), 43))) # Michael S. Branicky, Dec 27 2023