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 A231099 Primes expressible as phi(sigma(n)) + sigma(phi(n)), in order of their occurrence. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS K. D. Bajpai, Table of n, a(n) for n = 1..3500 EXAMPLE 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. MAPLE 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); CROSSREFS Cf. A062401 (phi(sigma(n))). Cf. A062402 (sigma(phi(n))). Sequence in context: A319126 A134266 A233043 * A062252 A153800 A147791 Adjacent sequences:  A231096 A231097 A231098 * A231100 A231101 A231102 KEYWORD nonn,less AUTHOR K. D. Bajpai, Nov 03 2013 STATUS approved

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Last modified June 22 12:56 EDT 2021. Contains 345380 sequences. (Running on oeis4.)