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A125237
Numbers n for which the absolute value of the abundance of both n and n^2 is a prime number.
3
3, 9, 10, 18, 50, 100, 104, 121, 136, 289, 464, 576, 650, 900, 5041, 6962, 7225, 10201, 14400, 55225, 65025, 87025, 102152, 147456, 171698, 174050, 179776, 182329, 189225, 201601, 222784, 291848, 312481, 380689, 410881, 469225, 481636, 488601
OFFSET
1,1
LINKS
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
Sequence in context: A134073 A088005 A340459 * A085459 A092169 A093108
KEYWORD
nonn
AUTHOR
Jason G. Wurtzel, Nov 25 2006
EXTENSIONS
More terms from Klaus Brockhaus, Nov 25 2006
STATUS
approved