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A337931 Number of ways to write n as the sum of two positive integers, s,t such that phi(s) is not equal to phi(t), where phi is the Euler totient function (A000010). 1
0, 0, 0, 1, 2, 2, 2, 3, 3, 3, 5, 5, 5, 6, 6, 6, 7, 7, 9, 8, 9, 9, 10, 11, 11, 12, 12, 13, 14, 14, 14, 14, 15, 15, 16, 16, 18, 18, 17, 18, 19, 20, 21, 20, 21, 20, 22, 23, 21, 23, 24, 25, 26, 24, 26, 27, 25, 27, 29, 29, 30, 29, 30, 30, 30, 31, 33, 32, 32, 33, 35, 34, 35, 34, 36, 37 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..76.

FORMULA

a(n) = Sum_{i=1..floor(n/2)} (1 - [phi(i) = phi(n-i)]), where phi is the Euler totient function (A000010) and [ ] is the Iverson bracket.

MATHEMATICA

Table[Sum[1 - KroneckerDelta[EulerPhi[i], EulerPhi[n - i]], {i, Floor[n/2]}], {n, 100}]

CROSSREFS

Cf. A000010, A337930.

Sequence in context: A285582 A032562 A076973 * A008649 A008650 A062051

Adjacent sequences:  A337928 A337929 A337930 * A337932 A337933 A337934

KEYWORD

nonn

AUTHOR

Wesley Ivan Hurt, Sep 30 2020

STATUS

approved

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Last modified August 6 00:36 EDT 2021. Contains 346493 sequences. (Running on oeis4.)