A036434 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

A036434

Integers which cannot be written as k+tau(k) for some k.

4

1, 3, 6, 8, 11, 16, 17, 20, 22, 23, 27, 29, 35, 36, 40, 41, 44, 46, 47, 53, 54, 57, 60, 65, 67, 68, 70, 76, 77, 79, 80, 83, 87, 88, 92, 93, 94, 100, 101, 106, 107, 114, 116, 117, 121, 125, 128, 131, 132, 134, 135, 140, 142, 148, 155, 156, 157, 158, 161, 164, 166

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

Invented by the HR concept formation program.

Indices of 0's in A036431. - Sean A. Irvine, Nov 01 2020

LINKS

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

Simon Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2 (1999), Article 99.1.2.

Simon Colton, HR - Automatic Theory Formation in Pure Mathematics.

EXAMPLE

None of 1,2,3,4,5,6,7 are such that k+tau(k)=8, so 8 is in the sequence.

MATHEMATICA

m = 200; Complement[Range[m], Table[n + DivisorSigma[0, n], {n, 1, m}]] (* Amiram Eldar, Nov 10 2021 *)

PROG

(PARI) isok(n) = sum(k=1, n, k+numdiv(k) != n) == n; \\ Michel Marcus, Dec 08 2014

CROSSREFS

Cf. A036431, A036438, A062249.

Sequence in context: A164910 A276583 A135736 * A298795 A140400 A190430

Adjacent sequences: A036431 A036432 A036433 * A036435 A036436 A036437

KEYWORD

nonn

AUTHOR

Simon Colton (simonco(AT)cs.york.ac.uk)

STATUS

approved