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A068146
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Primes of the form a^a - b^b.
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4
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3, 23, 229, 3121, 776887, 16774091, 275311670611, 302875106545597, 437893890380859119, 808793517812627212561, 827240252970236315921, 1978419655651397488675723, 20880467999847900922348207352551
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Charles R Greathouse IV, Table of n, a(n) for n = 1..76
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FORMULA
| The sum of the reciprocals converges to 0.38150016336280165719931278557192073226416041392427864458688292865... - Cino hilliard (hillcino368(AT)gmail.com), Dec 15 2002
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EXAMPLE
| 229 = 4^4 - 3^3 is a prime.
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MATHEMATICA
| Select[ Union[ Flatten[ Table[a^a - b^b, {a, 1, 40}, {b, 1, a - 1} ]]], PrimeQ ]
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PROG
| (PARI) v=[]; for(a=2, 400, forstep(b=a-1, 1, -2, if(ispseudoprime(t=a^a-b^b), v=concat(v, t)))); v \\ Charles R Greathouse IV, Feb 14 2011
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CROSSREFS
| Cf. A068145.
Sequence in context: A068955 A151393 A007781 * A162591 A122009 A151433
Adjacent sequences: A068143 A068144 A068145 * A068147 A068148 A068149
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Feb 23 2002
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EXTENSIONS
| Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com) and Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Mar 01 2002
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