OFFSET
1,1
COMMENTS
The subsequence of primes in this sequence begins: 101, 131, 167, 3067.
FORMULA
a(n) = SUM[i=1..n] {i such that 2^i - 1 is divisible by a square}.
EXAMPLE
a(20) = 6 + 12 + 18 + 20 + 21 + 24 + 30 + 36 + 40 + 42 + 48 + 54 + 60 + 63 + 66 + 72 + 78 + 80 + 84 + 90.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Feb 06 2010
EXTENSIONS
More terms from R. J. Mathar, Feb 16 2010
STATUS
approved