OFFSET
1,3
COMMENTS
Conjecture: sequence consists of an infinite number of subsequences S(m,0) = A172241(n) = (1/18)[8^n-(-1)^n-9], m>0, S(m,n+1) = 4*S(m,n)+1. The first subsequences
S(1,n) = A002450(n) = (4^n-1)/3 = 0, 1, 5, 21, 85, ...,
S(2,n) = A072197(n) = (10*4^n-1)/3 = 3, 13, 53, 213, ...,
S(3,n) = (85*4^n-1)/3 = 28, 113, 453, ...,
S(4,n) = (682*4^n-1)/3 = 227, 909, 3637, ..., and generally,
S(m,n) = [(3*A172241(m) + 1) * 4^n - 1]/3.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
seq[max_] := Module[{kmax = Floor[Log[4, 3*max+1]], s = {}, s1, odd}, Do[odd = (4^k-1)/3; s1 = 2^Range[0, Floor[Log2[max/odd]]] * odd; s = Join[s, s1], {k, 1, kmax}]; Select[(Union[s] - 1)/3, IntegerQ]]; seq[10^7] (* Amiram Eldar, Sep 01 2024 *)
PROG
(PARI) for(n=1, 300000, o=3*n/2^valuation(n, 2)+1; b=ispower(o); if(b&&b%2==0&&round(sqrtn(o, b/2))==4&&(n-1)%3==0, print1((n-1)/3, ", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Nov 19 2010
EXTENSIONS
More terms from Amiram Eldar, Sep 01 2024
STATUS
approved