OFFSET
0,1
COMMENTS
If a(n) == 0 (mod 2), then a(n+1) = a(n)/2.
Records: 5, 7, 9, 15, 25, 35, 52, 84, 104, 146, 284, 330, 645, 660, 1020, 1677, 1701, 1747, 2247, 2991, ..., .
Corresponding primes are twin primes for n = 0, 1, 2, 3, 8, 17, 18, 19, 23, 43, 44, 64, 156, 189, 190, 210, 211, 212, 264, 265, 281, 282, 283, 388, 547, 725, 726, 727, ..., .
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 0..1000
MATHEMATICA
f[n_] := Block[{k = 1, j = 2^n/2}, While[ h = k*j; PrimeQ@h || NextPrime[h, -1] + NextPrime@h != 2 h, k++ ]; k]; Array[f, 79, 0]
PROG
(Python)
from sympy import isprime, nextprime, prevprime
def ok(n):
if n <= 5: return n == 5
return not isprime(n//2) and n == prevprime(n//2) + nextprime(n//2)
def a(n):
k, pow2 = 1, 2**n
while not ok(k*pow2): k += 1
return k
print([a(n) for n in range(79)]) # Michael S. Branicky, May 04 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov & Robert G. Wilson v, Aug 15 2010
STATUS
approved