A194579 Numbers whose sum of the their nonprime divisors is prime.

4, 6, 8, 10, 12, 16, 22, 27, 28, 32, 40, 44, 46, 52, 58, 68, 80, 82, 88, 106, 112, 116, 124, 125, 136, 148, 164, 165, 166, 172, 176, 178, 192, 208, 226, 232, 236, 250, 256, 262, 284, 292, 304, 316, 328, 332, 346, 352, 358, 368, 382, 388, 420, 428, 435

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

The divisors of 28 are {1, 2, 4, 7, 14, 28} and the sum of its nonprime divisors is 1 + 4 + 14 + 28 = 47 is prime, hence 28 is in the sequence.

Maple

with(numtheory): for n from 1 to 435 do x:=divisors(n): n1:=nops(x): s:=0: for k from 1 to n1 do if not isprime(x[k]) then s:=s+x[k] fi od: if isprime(s) then printf(`%d, `, n) fi od:

Mathematica

f[n_] := Plus @@ Select[Divisors[n], ! PrimeQ[#] &]; Select[Range[435], PrimeQ[f[#]] &] (* T. D. Noe, Aug 29 2011 *)

Prog

(PARI) isok(n) = isprime(sumdiv(n, d, if (!isprime(d), d))); \\ Michel Marcus, Jan 07 2020

Crossrefs

Cf. A194594.

Sequence in context: A309837 A310659 A076298 * A194594 A163248 A341280

Adjacent sequences: A194576 A194577 A194578 * A194580 A194581 A194582

Keyword

nonn

Author

Michel Lagneau, Aug 29 2011

Status

approved