OFFSET
1,1
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10203
EXAMPLE
4 is in the sequence because sigma(4) = 7 and sigma(4^2) = 31 are both primes.
MATHEMATICA
Select[Range[10^4], AllTrue[DivisorSigma[1, #] & /@ {#, #^3}, PrimeQ] &] (* Michael De Vlieger, Feb 05 2018 *)
PROG
(Magma) [n: n in[1..10000000] | IsPrime(SumOfDivisors(n)) and IsPrime(SumOfDivisors(n^3))]
(PARI) isok(n) = isprime(sigma(n)) && isprime(sigma(n^3)); \\ Michel Marcus, Feb 05 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Feb 03 2018
STATUS
approved