OFFSET
1,1
COMMENTS
Number of terms <= 2^k: 0, 0, 1, 3, 5, 9, 13, 19, 25, 36, 47, 65, 83, 114, 145, 199, 253, 350, 447, …, .
Number of terms <= 2^k = Sum {i=2..k}, PrimePi( If( k < n/2, 2^k, 2^(n - k))).
Conjecture: a subsequence of A116882;
Terms in A116882 but not here: 1, 2, 4, 144, 240, 288, 480, 576, 672, 800, 864, 960, 1152, ... ; or more simply 1, 2, 4 and powers of 2 times 144, 240, 672, 800, 864, 2112, 2240, 2496, 2880, 3136, ...
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 1..1000
MATHEMATICA
f[n_] := Block[{p = Prime@ Range@ PrimePi[2^n - 1]}, 2^n* p]; Take[ Sort@ Flatten@ Array[f, 10], 57]
PROG
(PARI) isok(n) = my(m = valuation(n, 2)); (isprime(p=n/2^m) && (p < 2^m)) || ((m > 2) && (n==2^m)); \\ Michel Marcus, Aug 31 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, May 30 2016
STATUS
approved