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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
OFFSET
1,1
LINKS
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 A362777
KEYWORD
nonn,less
AUTHOR
K. D. Bajpai, Nov 03 2013
STATUS
approved