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A333838 a(n) is the greatest integer q <= r such that for some r, phi(q) + phi(r) = 2*n. 0
1, 0, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 12, 14, 15, 16, 17, 18, 19, 20, 21, 21, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 34, 38, 39, 40, 41, 42, 43, 43, 45, 46, 47, 48, 49, 50, 51, 52, 53, 53, 55, 56, 57, 58, 59, 60, 60, 61, 62, 64, 65, 66, 64, 68, 68, 70 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Paul Erdős and Leo Moser conjectured that, for any even numbers 2*n, there exist integers q and r such that phi(q) + phi(r) = 2*n.

REFERENCES

George E. Andrews, Number Theory, Chapter 6, Arithmetic Functions, 6-1 Combinatorial Study of Phi(n) page 75-82, Dover Publishing, NY, 1971.

Daniel Zwillinger, Editor-in-Chief, CRC Standard Mathematical Tables and Formulae, 31st Edition, 2.4.15 Euler Totient pages 128-130, Chapman & Hall/CRC, Boca Raton, 2003.

LINKS

Table of n, a(n) for n=1..70.

Eric W. Weisstein's World of Mathematics, Goldbach's Conjecture.

Wikipedia, Goldbach's conjecture

Index entries for sequences related to Goldbach conjecture

MATHEMATICA

mbr = Union@Array[EulerPhi@# &, 500]; a[n_] := Block[{q = n}, While[! MemberQ[mbr, 2 n - EulerPhi@q], q--]; q]; Array[a, 70]

CROSSREFS

Cf. A306513, A306513, A333819, A333820.

Sequence in context: A118716 A004177 A004721 * A030544 A141213 A171950

Adjacent sequences:  A333835 A333836 A333837 * A333839 A333840 A333841

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Apr 07 2020

STATUS

approved

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Last modified June 17 00:17 EDT 2021. Contains 345080 sequences. (Running on oeis4.)