

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
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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, AppendTo[s, n1]], {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



