OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..500
EXAMPLE
n=3: The abundance of 3 is -2, the negative of a prime. n^2=9, the abundance of 9 is -5, the negative of a prime as well.
MATHEMATICA
pQ[n_] := PrimeQ[DivisorSigma[1, n] - 2n]; Select[Range[10^4], pQ[#] && pQ[#^2] &] (* Amiram Eldar, Sep 24 2019 *)
PROG
(PARI) {for(n=1, 500000, if(isprime(abs(sigma(n)-2*n)) && isprime(abs(sigma(n^2)-2*n^2)), print1(n, ", ")))} \\ Klaus Brockhaus, Nov 25 2006
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason G. Wurtzel, Nov 25 2006
EXTENSIONS
More terms from Klaus Brockhaus, Nov 25 2006
STATUS
approved