A118854 - OEIS

A118854

Numbers m such that m-1 and m have the same number of common totatives as m and m+1 have.

2, 3, 8, 21, 24, 27, 45, 75, 93, 105, 117, 123, 147, 165, 213, 309, 315, 333, 357, 387, 453, 525, 555, 573, 627, 636, 693, 717, 729, 765, 795, 843, 915, 933, 957, 1005, 1083, 1125, 1173, 1227, 1323, 1347, 1437, 1467, 1515, 1563, 1575, 1677, 1725, 1755, 1773

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OFFSET

1,1

COMMENTS

A057475(a(n)-1) = A057475(a(n));

it seems that even values are very rare, see A118855.

LINKS

Table of n, a(n) for n=1..51.

Eric Weisstein's World of Mathematics, Totative

EXAMPLE

n = 21, the sets of totatives for 21-1, 21 and 21+1:

T(20) = {1,3,7,9,11,13,17,19},