A260020 Numbers n such that 2*phi(n) = phi(2*sigma(n)).

2, 3, 8, 9, 15, 26, 39, 45, 74, 104, 111, 117, 122, 128, 146, 175, 183, 195, 219, 296, 314, 333, 357, 386, 471, 488, 549, 554, 555, 579, 584, 585, 608, 626, 646, 657, 794, 831, 842, 914, 915, 939, 962, 1071, 1082, 1095, 1191, 1226, 1256, 1263, 1292, 1322

Offset: 1

Author

N. J. A. Sloane, Jul 14 2015

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• S. W. Golomb, Equality among number-theoretic functions, Unpublished manuscript. (Annotated scanned copy)

Crossrefs

Cf. A006872.

Cf. A000010, A000203.

Programs

Haskell

a260020 n = a260020_list !! (n-1)
a260020_list = filter
               (\x -> 2 * a000010' x == a000010' (2 * a000203' x)) [1..]
-- Reinhard Zumkeller, Jul 14 2015