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A292770 If sigma(n)+phi(n) is even then (sigma(n)+phi(n))/2 otherwise -1. 2
1, 2, 3, -1, 5, 7, 7, -1, -1, 11, 11, 16, 13, 15, 16, -1, 17, -1, 19, 25, 22, 23, 23, 34, -1, 27, 29, 34, 29, 40, 31, -1, 34, 35, 36, -1, 37, 39, 40, 53, 41, 54, 43, 52, 51, 47, 47, 70, -1, -1, 52, 61, 53, 69, 56, 72, 58, 59, 59, 92, 61, 63, 70, -1, 66, 82, 67, 79, 70, 84, 71, -1, 73, 75, 82, 88, 78, 96 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

MAPLE

f:= proc(n) local v;

   v:= numtheory:-sigma(n)+numtheory:-phi(n);

   if v::even then v/2 else -1 fi

end proc:

map(f, [$1..100]); # Robert Israel, Sep 28 2017

CROSSREFS

Cf. A065387, A291790, A292108, A292766, A000010, A000203, A292771.

Sequence in context: A071975 A182659 A197701 * A242107 A242108 A238941

Adjacent sequences:  A292767 A292768 A292769 * A292771 A292772 A292773

KEYWORD

sign

AUTHOR

N. J. A. Sloane, Sep 28 2017

STATUS

approved

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Last modified October 28 18:13 EDT 2021. Contains 348329 sequences. (Running on oeis4.)