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A194579 Numbers n such that the sum of the their nonprime divisors is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..55.

EXAMPLE

The divisors of 28 are {1, 2, 4, 7, 14, 28} and the sum of the nonprime divisors 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 *)

CROSSREFS

Sequence in context: A075027 A310659 A076298 * A194594 A163248 A034288

Adjacent sequences:  A194576 A194577 A194578 * A194580 A194581 A194582

KEYWORD

nonn

AUTHOR

Michel Lagneau, Aug 29 2011

STATUS

approved

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Last modified May 21 00:41 EDT 2019. Contains 323427 sequences. (Running on oeis4.)