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A307055 Even k such that psi(m) = k has no solution, where psi is the Dedekind psi function A001615. 2
2, 10, 16, 22, 26, 28, 34, 40, 46, 50, 52, 58, 64, 66, 70, 76, 78, 82, 86, 88, 92, 94, 100, 106, 116, 118, 122, 124, 130, 134, 136, 142, 146, 148, 154, 156, 166, 170, 172, 178, 184, 188, 190, 196, 202, 206, 208, 210, 214, 218, 220, 226, 232, 236, 238, 244, 246, 250 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Analog of the nontotients A005277.

Contains 2*p if p is in A307390. - Robert Israel, Apr 17 2019

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

2 is a term because there exists no m such that psi(m) = 2.

4 is not a term because 4 = 3*(3+1)/3.

MAPLE

N:= 1000: # to get all terms <= N

psi:= proc(n) local p; n*mul(1+1/p, p=numtheory:-factorset(n)) end proc:

sort(convert({seq(i, i=2..N, 2)} minus map(psi, {$1..N}), list)); # Robert Israel, Apr 17 2019

MATHEMATICA

M = 1000; (* to get all terms <= M *)

psi[n_] := n Sum[MoebiusMu[d]^2/d, {d, Divisors[n]}];

Range[2, M, 2] ~Complement~ (psi /@ Range[M]) (* Jean-Fran├žois Alcover, Aug 01 2020, after Maple *)

PROG

(PARI) dpsi(n) = = n * sumdivmult(n, d, issquarefree(d)/d); \\ A001615

isok(n) = {if (!(n%2), for (k=1, n-1,  if (dpsi(k) == n, return(0)); ); return (1); ); } \\ Michel Marcus, Mar 22 2019

CROSSREFS

Cf. A001615, A005277, A005382.

Sequence in context: A105041 A138632 A175957 * A060658 A239321 A054028

Adjacent sequences:  A307052 A307053 A307054 * A307056 A307057 A307058

KEYWORD

nonn

AUTHOR

Torlach Rush, Mar 21 2019

STATUS

approved

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Last modified October 1 15:55 EDT 2020. Contains 337443 sequences. (Running on oeis4.)