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 A086470 Numbers k such that psigma(k) = psigma(k+1), where psigma(k) = A086469(k). 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If n =3p and n+1 = 2q where p and q are primes then n is a member. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 EXAMPLE 9 is a member as psigma(9) = 1+3 +9 = psigma(10) = 1+2 +10 = 13. MATHEMATICA 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 *) CROSSREFS Cf. A086469. Sequence in context: A243703 A133929 A325573 * A176256 A017629 A216240 Adjacent sequences:  A086467 A086468 A086469 * A086471 A086472 A086473 KEYWORD nonn AUTHOR Amarnath Murthy, Jul 21 2003 EXTENSIONS Corrected and extended by David Wasserman, Mar 07 2005 Offset corrected by Amiram Eldar, Jul 20 2019 STATUS approved

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Last modified October 5 01:17 EDT 2022. Contains 357240 sequences. (Running on oeis4.)