A078762 Numbers n such that n + sigma(n) is prime.

1, 2, 3, 4, 5, 8, 11, 16, 21, 23, 27, 29, 35, 36, 41, 53, 55, 57, 63, 64, 65, 75, 77, 83, 85, 89, 98, 100, 111, 113, 119, 125, 128, 131, 133, 143, 144, 155, 161, 171, 173, 179, 183, 189, 191, 203, 205, 209, 215, 233, 235, 237, 239, 242, 243, 245, 251, 253, 259, 275

Offset: 1

Author

Joseph L. Pe, Jan 08 2003

Keywords

• nonn
• easy

Comments

Union of A005384 (Sophie Germain primes) and A249486. - Jaroslav Krizek, Nov 13 2014

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Programs

Maple

select(t -> isprime(t+numtheory:-sigma(t)), [$1..1000]); # Robert Israel, May 01 2018

Mathematica

Select[Range[10^3], PrimeQ[ # + DivisorSigma[1, # ]] &]

PARI

for(n=1,1000,if(isprime(sigma(n)+n),print1(n,", "))) \\ Derek Orr, Nov 13 2014