login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A276674 Numbers n such that x - lambda(x) = n has no solution, where lambda(x) = A002322(x). 0
21, 28, 45, 46, 51, 64, 65, 77, 82, 85, 91, 106, 111, 126, 129, 133, 136, 148, 155, 166, 172, 175, 185, 189, 205, 208, 209, 217, 221, 225, 231, 232, 235, 237, 244, 247, 267, 273, 274, 276, 286, 291, 298, 305, 316, 319, 326, 333, 339, 341, 358, 362, 364, 365, 371 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Problem: are there infinitely many such numbers?

Note that all these numbers are composite, because p - lambda(p) = 1 and p^2 - lambda(p^2) = p prime.

If x - lambda(x) = n > 1, then x <= n^2.

Conjecture: if x - lambda(x) = 2*m > 0, then x <= 4*m.

Noncototients among these numbers are 172, 232, 244, 274, 298, 326, 362, ...

LINKS

Table of n, a(n) for n=1..55.

PROG

(PARI) lista(nn) = {v = vecsort(vector(nn^2, n, n - lcm(znstar(n)[2])), , 8); for (n=1, nn, if (! vecsearch(v, n), print1(n, ", ")); ); } \\ Michel Marcus, Oct 03 2016

(Perl) use ntheory ":all"; sub A { my $l=shift; my %C; undef $C{$_-carmichael_lambda($_)} for 1..$l*$l; my @R = grep { !exists $C{$_} } 1..$l; @R; } say for A(500); # Dana Jacobsen, Apr 27 2017

CROSSREFS

Cf. A002322, A005278 (see links). Complement of A277127.

Sequence in context: A227936 A048012 A254368 * A130202 A162692 A048067

Adjacent sequences:  A276671 A276672 A276673 * A276675 A276676 A276677

KEYWORD

nonn

AUTHOR

Thomas Ordowski, Oct 03 2016

EXTENSIONS

More terms from Michel Marcus, Oct 03 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified September 20 12:31 EDT 2017. Contains 292271 sequences.