0,3

The next term is too large to include.

Last digit of a(n) is 5 or 9 for n>1. It appears that a(4k) == 4 mod 5 and a(4k+1) == a(4k+2) == a(4k+3) == 0 mod 5.

p divides a(p) for prime p>2. Composite numbers n such that n divides a(n) are listed in A127643 = {15,51,65,85,185,221,255,341,451,533,561,595,645,679,771,...}. - Alexander Adamchuk (alex(AT)kolmogorov.com), Jan 22 2007

a(n) = ((2^n - 1)^(2^n) - 1)/(2^n)^2. a(n) = A085606[2^n]/(2^n)^2.

Table[((2^n-1)^(2^n)-1)/(2^n)^2, {n, 0, 7}]

Cf. A085606 (n-1)^n - 1.

Cf. A127643.

Sequence in context: A013834 A055380 A050816 this_sequence A133381 A038027 A057679

Adjacent sequences: A123588 A123589 A123590 this_sequence A123592 A123593 A123594

sign

Alexander Adamchuk (alex(AT)kolmogorov.com), Nov 13 2006

More terms from Alexander Adamchuk (alex(AT)kolmogorov.com), Jan 22 2007