OFFSET
1,1
COMMENTS
Subsequence of A004215.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = max_{2<=i<=n+1, j>=0} {4^i*(8j+7) : 4^i*(8j+7) < 3^(2n+5)}.
EXAMPLE
2160 is not the sum of 3 squares and a nonnegative 7th power, and all integers larger than 2160 can be represented as the sum of 3 squares and a nonnegative 7th power (see A297970). Thus a(1) = 2160.
MATHEMATICA
a[n_]:= Max@Table[4^k (8 Floor[3^(2 n + 5) / 2^(2 k + 3) - 7 / 8] + 7), {k, 2, n + 1}] Table[a[n], {n, 18}] (* XU Pingya, Nov 30 2018 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
XU Pingya, Feb 19 2018
STATUS
approved