A343151 Numbers k such that 1+A083266(k) is prime.

1, 3, 4, 7, 8, 11, 19, 23, 25, 27, 36, 43, 47, 50, 64, 71, 107, 131, 163, 167, 179, 211, 223, 225, 242, 243, 251, 271, 307, 343, 359, 419, 431, 439, 443, 467, 503, 571, 691, 751, 800, 811, 827, 839, 863, 900, 907, 947, 967, 971, 991, 1019, 1031, 1058, 1063, 1091, 1103, 1187, 1279, 1296, 1331

Offset: 1

Author

J. M. Bergot and Robert Israel, Apr 07 2021

Keywords

• nonn

Comments

Numbers k such that the sum of divisors of k + the sum of totatives of k is prime.

Examples

			a(4) = 7 is a term because 1+A083266(n) = 29 is prime.
		

Links

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

Crossrefs

Cf. A083266, A343148. Includes A231847.

Programs

Maple

f:= n -> numtheory:-sigma(n) + n*numtheory:-phi(n)/2: f(1):= 2:
select(t -> isprime(f(t)), [$1..2000]);

Mathematica

{1}~Join~Select[Range[1331], PrimeQ[DivisorSigma[1, #] + # EulerPhi[#]/2] &] (* Michael De Vlieger, Apr 07 2021 *)