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A231099
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Primes expressible as phi(sigma(n)) + sigma(phi(n)), in order of their occurrence.
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1
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2, 3, 5, 7, 13, 19, 23, 37, 47, 31, 67, 109, 71, 79, 139, 127, 139, 163, 227, 199, 443, 379, 313, 271, 547, 367, 619, 547, 593, 643, 523, 739, 619, 1093, 883, 691, 907, 787, 1153, 787, 787, 787, 1867, 1327, 1987, 1231, 1487, 1487, 2731, 2659, 2551, 4327, 4231
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(6)= 19: phi(sigma(12)) + sigma(phi(12))= 12+7= 19 which is prime.
a(9)= 47: phi(sigma(19)) + sigma(phi(19))= 8+39= 47 which is prime.
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MAPLE
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with(numtheory): KD:= proc() local a; a:= phi(sigma(n))+sigma(phi(n)); if isprime(a) then return (a) : fi; end: seq(KD(), n=1..10000);
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CROSSREFS
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KEYWORD
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nonn,less
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AUTHOR
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STATUS
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approved
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