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A200981 Numbers n such that the sum of non-divisors of n is prime. 2
3, 4, 10, 21, 34, 46, 58, 70, 85, 93, 118, 129, 130, 144, 178, 201, 226, 237, 262, 298, 310, 322, 324, 325, 333, 334, 346, 382, 406, 418, 430, 466, 478, 502, 513, 514, 517, 549, 598, 622, 633, 634, 657, 658, 669, 706, 730, 742, 813, 826, 837, 838 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..10000

EXAMPLE

Non-divisors of 10 are 3, 4, 6, 7, 8, 9 and their sum is 37 that is prime.

MAPLE

with(numtheory);

P:=proc(i)

local a, n;

for n from 1 to i do

  a:=n*(n+1)/2-sigma(n); if isprime(a) then print(n); fi;

od;

end:

P(1000000);

MATHEMATICA

okQ[n_] := (n > 0) && PrimeQ[n]; Select[Range[1000], okQ[# (#+1)/2 - DivisorSigma[1, #]] &] (* T. D. Noe, Dec 15 2011 *)

CROSSREFS

Cf. A023194, A024816.

Sequence in context: A036649 A255539 A109887 * A266729 A103038 A143108

Adjacent sequences:  A200978 A200979 A200980 * A200982 A200983 A200984

KEYWORD

nonn,easy

AUTHOR

Paolo P. Lava, Dec 13 2011

STATUS

approved

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Last modified July 25 04:48 EDT 2017. Contains 289779 sequences.