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A086470
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Numbers k such that psigma(k) = psigma(k+1), where psigma(k) = A086469(k).
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2
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9, 21, 33, 44, 57, 93, 141, 169, 177, 201, 213, 258, 381, 393, 426, 453, 501, 537, 633, 670, 678, 717, 762, 921, 933, 1041, 1137, 1266, 1293, 1317, 1401, 1437, 1590, 1641, 1686, 1713, 1761, 1821, 1857, 1893, 1941, 1990, 2181, 2217, 2361, 2433, 2509, 2517
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OFFSET
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1,1
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COMMENTS
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If n =3p and n+1 = 2q where p and q are primes then n is a member.
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LINKS
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EXAMPLE
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9 is a member as psigma(9) = 1+3 +9 = psigma(10) = 1+2 +10 = 13.
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MATHEMATICA
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a[n_] := Module[{d = Rest[Divisors[n]]}, 1 + Total@DeleteDuplicatesBy[{#, Sort[FactorInteger[#][[;; , 2]]]} & /@ d, Last][[;; , 1]]]; s={}; a1=0; Do[a2 = a[n]; If[a1 == a2, Append|To[s, n-1]], {n, 1, 2500}]; s (* Amiram Eldar, Jul 20 2019 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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