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.

Showing 1-3 of 3 results.

A036378 Number of primes p between powers of 2, 2^n < p <= 2^(n+1).

Original entry on oeis.org

1, 1, 2, 2, 5, 7, 13, 23, 43, 75, 137, 255, 464, 872, 1612, 3030, 5709, 10749, 20390, 38635, 73586, 140336, 268216, 513708, 985818, 1894120, 3645744, 7027290, 13561907, 26207278, 50697537, 98182656, 190335585, 369323305, 717267168, 1394192236, 2712103833
Offset: 0

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Keywords

Comments

Number of primes whose binary order (A029837) is n+1, i.e., those with ceiling(log_2(p)) = n+1. [corrected by Jon E. Schoenfield, May 13 2018]
First differences of A007053. This sequence illustrates how far the Bertrand postulate is oversatisfied.
Scaled for Ramanujan primes as in A190501, A190502.
This sequence appears complete such that any nonnegative number can be written as a sum of distinct terms of this sequence. The sequence has been checked for completeness up to the gap between 2^46 and 2^47. Assuming that after 2^46 the formula x/log(x) is a good approximation to primepi(x), it can be proved that 2*a(n) > a(n+1) for all n >= 46, which is a sufficient condition for completeness. [Frank M Jackson, Feb 02 2012]

Examples

			The 7 primes for which A029837(p)=6 are 37, 41, 43, 47, 53, 59, 61.
		

Crossrefs

Programs

  • Magma
    [1,1] cat [#PrimesInInterval(2^n, 2^(n+1)): n in [2..29]]; // Vincenzo Librandi, Nov 18 2014
  • Mathematica
    t = Table[PrimePi[2^n], {n, 0, 20}]; Rest@t - Most@t (* Robert G. Wilson v, Mar 20 2006 *)
  • PARI
    a(n) = primepi(1<<(n+1))-primepi(1<
    				

Formula

a(n) = primepi(2^(n+1)) - primepi(2^n).
a(n) = A095005(n)+A095006(n) = A095007(n) + A095008(n) = A095013(n) + A095014(n) = A095015(n) + A095016(n) (for n > 1) = A095021(n) + A095022(n) + A095023(n) + A095024(n) = A095019(n) + A095054(n) = A095020(n) + A095055(n) = A095060(n) + A095061(n) = A095063(n) + A095064(n) = A095094(n) + A095095(n).

Extensions

More terms from Labos Elemer, May 13 2004
Entries checked by Robert G. Wilson v, Mar 20 2006

A095083 Fibodious primes, i.e., primes p whose Zeckendorf-expansion A014417(p) contains an odd number of 1-fibits.

Original entry on oeis.org

2, 3, 5, 13, 17, 19, 31, 41, 43, 59, 61, 71, 73, 79, 89, 103, 107, 113, 131, 151, 167, 173, 179, 181, 191, 197, 211, 227, 229, 233, 239, 251, 257, 269, 293, 307, 313, 347, 349, 353, 367, 383, 401, 419, 431, 433, 449, 457, 463, 467, 479, 487, 491
Offset: 1

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Author

Antti Karttunen, Jun 01 2004

Keywords

Crossrefs

Intersection of A000040 and A020899.

Programs

  • Mathematica
    Select[Flatten[Position[Mod[DigitCount[Select[Range[0, 5000], BitAnd[#, 2 #] == 0 &], 2, 1], 2], 1]] - 1, PrimeQ] (* Amiram Eldar, Feb 07 2023 *)
  • Python
    from sympy import fibonacci, primerange
    def a(n):
        k=0
        x=0
        while n>0:
            k=0
            while fibonacci(k)<=n: k+=1
            x+=10**(k - 3)
            n-=fibonacci(k - 1)
        return x
    def ok(n): return str(a(n)).count("1")%2
    print([n for n in primerange(1, 1001) if ok(n)]) # Indranil Ghosh, Jun 08 2017

A095064 Number of fibevil primes (A095084) in range ]2^n,2^(n+1)].

Original entry on oeis.org

0, 1, 1, 2, 3, 6, 9, 21, 34, 67, 122, 203, 439, 812, 1562, 2826, 5304, 10357, 19247, 36684, 70168, 134211, 256937, 492730, 946967, 1823368, 3512484, 6781240, 13103839, 25345814, 49096941, 95168742, 184666456, 358645108, 697065364
Offset: 1

Views

Author

Antti Karttunen, Jun 01 2004

Keywords

Crossrefs

Formula

a(n) = A036378(n) - A095063(n).

Extensions

a(34)-a(35) from Amiram Eldar, Jun 13 2024
Showing 1-3 of 3 results.