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 A123591 a(n) = ((2^n - 1)^(2^n) - 1)/(2^n)^2. 2
 -1, 0, 5, 90075, 25657845139503479, 516742576223066713590751888575037849059948015 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 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, Jan 22 2007 LINKS G. C. Greubel, Table of n, a(n) for n = 0..8 FORMULA a(n) = ((2^n - 1)^(2^n) - 1)/(2^n)^2. a(n) = A085606(2^n)/(2^n)^2. MATHEMATICA Table[((2^n-1)^(2^n)-1)/(2^n)^2, {n, 0, 7}] PROG (PARI) for(n=0, 7, print1(((2^n - 1)^(2^n) - 1)/(2^n)^2, ", ")) \\ G. C. Greubel, Oct 26 2017 (MAGMA) [((2^n - 1)^(2^n) - 1)/(2^n)^2: n in [0..7]]; // G. C. Greubel, Oct 26 2017 CROSSREFS Cf. A085606 (n-1)^n - 1. Cf. A127643. Sequence in context: A171981 A145232 A263174 * A133381 A236066 A151589 Adjacent sequences:  A123588 A123589 A123590 * A123592 A123593 A123594 KEYWORD sign AUTHOR Alexander Adamchuk, Nov 13 2006 EXTENSIONS More terms from Alexander Adamchuk, Jan 22 2007 STATUS approved

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Last modified October 14 04:28 EDT 2019. Contains 327995 sequences. (Running on oeis4.)