A249671 Integers n such that A249670(n) = n.

1, 364, 86800, 90768, 149856, 632400, 828816, 46462800, 61987600, 148468320, 153972000, 185684160, 187465824, 189300384, 191659104, 193808160, 196219296, 202460352, 204118464, 215399520, 220116960, 221931360, 222778080, 223382880, 228584160, 338116680

Offset

1,2

Comments

That is, integers n such that A017665(n)*A017666(n) = n.

Links

Table of n, a(n) for n=1..26.

Example

sigma(364)/364 = 28/13 and 28*13 = 364, so 364 is in the sequence.

Mathematica

lista[n_Integer] := Select[Range[n], # == Numerator[DivisorSigma[-1, #]] * Denominator[DivisorSigma[-1, #]] &];
lista[10^6] (* Michael De Vlieger, Nov 10 2014 *)

Prog

(PARI) isok(n) = my(ab = sigma(n)/n); numerator(ab)*denominator(ab) == n; \\ Michel Marcus, Nov 04 2014

Crossrefs

Cf. A017665, A017666, A249670.

Sequence in context: A329187 A107509 A140935 * A022196 A098252 A221393

Adjacent sequences: A249668 A249669 A249670 * A249672 A249673 A249674

Keyword

nonn

Author

Michel Marcus, Nov 03 2014

Status

approved