OFFSET
1,1
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..1020
EXAMPLE
a(6)= 631: phi(sigma(17))= 6. sigma(phi(17))= 31. After concatenating gives 631 which is prime.
a(9)= 1831: phi(sigma(34))= 18. sigma(phi(34))= 31. After concatenating gives 1831 which is prime.
MAPLE
with(numtheory): with(StringTools): KD:= proc() local a; a:= parse(cat(phi(sigma(n)), sigma(phi(n)))); if isprime(a) then return (a) : fi; end: seq(KD(), n=1..10000);
MATHEMATICA
ccpr[n_]:=Module[{a=EulerPhi[DivisorSigma[1, n]], b= DivisorSigma[1, EulerPhi[n]]}, FromDigits[Join[IntegerDigits[a], IntegerDigits[b]]]]; Select[Array[ccpr, 3000], PrimeQ] (* Harvey P. Dale, Apr 18 2014 *)
CROSSREFS
KEYWORD
nonn,base,less
AUTHOR
K. D. Bajpai, Nov 03 2013
STATUS
approved