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A238194 Conjectured numbers n for which n^n + (-1)^n (n-1)^(n-1) is not squarefree. 2
130, 257, 487, 528, 815, 897, 1176, 1225, 1320, 1373, 1430, 2029, 2050, 2084, 2198, 2247, 2526, 2608, 2895, 2936, 2958, 3166, 3679, 3849, 3909, 3950, 4237, 4319, 4598, 4647, 4723, 4795, 5472, 5487, 5620, 5669, 5948, 6030, 6317, 6358, 6588, 6677, 6936, 7101 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first case (130) yields a number divisible by 83^2. The next 5 terms yield numbers divisible by 59^2. Boyd et al. are not completely certain about the other 994 numbers up to 1000. They conjecture that 0.9934466... of numbers n^n + (-1)^n (n-1)^(n-1) are squarefree.

Boyd et al. tested the values n <= 1000 for divisibility by the squares of the first 10^4 primes. To extend the sequence, I tested the divisibility of n <= 200000 by the squares of the first 10^5 primes. - Giovanni Resta, Feb 24 2014

The heuristic chance that Resta's list is incomplete is just over 1%. This drops to 0.07% with testing to the millionth prime. - Charles R Greathouse IV, Feb 25 2014

LINKS

Table of n, a(n) for n=1..44.

David W. Boyd, Greg Martin, and Mark Thom, Squarefree values of trinomial discriminants, arXiv 1402.5148 [math.NT], 2014.

Giovanni Resta, Terms < 200000 and corresponding square divisors

PROG

(PARI) is(n)=!issquarefree(n^n + (-1)^n*(n-1)^(n-1)) \\ Charles R Greathouse IV, Feb 25 2014

CROSSREFS

Cf. A086797 (n^n + (-1)^n (n-1)^(n-1) with signs).

Sequence in context: A138481 A167702 A064687 * A252263 A252361 A252082

Adjacent sequences:  A238191 A238192 A238193 * A238195 A238196 A238197

KEYWORD

nonn,hard

AUTHOR

T. D. Noe, Feb 24 2014

EXTENSIONS

a(7)-a(44) from Giovanni Resta, Feb 24 2014

STATUS

approved

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Last modified December 14 14:20 EST 2019. Contains 329979 sequences. (Running on oeis4.)