A330703 Numbers k such that psi(k) = psi(k + 2) where psi(k) is the Dedekind psi function (A001615).

6, 9, 12, 14, 18, 20, 33, 44, 62, 70, 92, 108, 116, 138, 164, 175, 212, 254, 280, 308, 320, 332, 348, 356, 452, 490, 524, 558, 572, 692, 716, 764, 833, 932, 956, 1004, 1105, 1124, 1172, 1188, 1436, 1496, 1562, 1593, 1676, 1724, 1772, 1964, 2002, 2036, 2088, 2132

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Jozsef Sandor, On the composition of some arithmetic functions, II, Journal of Inequalities in Pure and Applied Mathematics, Vol. 6, No. 3 (2005), Article 73.

Example

6 is in the sequence since psi(6) = psi(8) = 12.

Mathematica

psi[1] = 1; psi[n_] := n * Times @@ (1 + 1/Transpose[FactorInteger[n]][[1]]); Select[Range[10^3], psi[#] == psi[# + 2] &]

Crossrefs

Cf. A001494, A001615, A007373, A062832, A291043.

Sequence in context: A295670 A272466 A267918 * A262828 A306647 A189728

Adjacent sequences: A330700 A330701 A330702 * A330704 A330705 A330706

Keyword

nonn

Author

Amiram Eldar, Dec 26 2019

Status

approved