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A194579
Numbers whose sum of the their nonprime divisors is prime.
2
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
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
KEYWORD
nonn
AUTHOR
Michel Lagneau, Aug 29 2011
STATUS
approved

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Last modified September 20 05:38 EDT 2024. Contains 376016 sequences. (Running on oeis4.)