login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A292005 Composite numbers n such that psi(n - phi(n)) = phi(psi(n) - n). 0
35, 65, 77, 161, 185, 209, 221, 335, 341, 371, 377, 437, 485, 515, 611, 671, 707, 731, 767, 779, 851, 899, 917, 965, 1007, 1067, 1115, 1157, 1211, 1247, 1271, 1337, 1385, 1397, 1529, 1535, 1577, 1631, 1691, 1781, 1817, 1841, 1991, 2117, 2171, 2201, 2285, 2291, 2327 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

10217383 = 11*19^2*31*83 is the smallest term that is not squarefree.

A176875 is a subsequence.

LINKS

Table of n, a(n) for n=1..49.

EXAMPLE

77 = 7*11 is a term because 77 - phi(77) = 17, psi(77) - 77 = 19 and phi(19) = psi(17).

PROG

(PARI) a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));

isok(n) = !isprime(n) && a001615(n-eulerphi(n))==eulerphi(a001615(n)-n); \\ after Charles R Greathouse IV at A001615

CROSSREFS

Cf. A000010, A001615, A176875, A290002.

Sequence in context: A092256 A108172 A176875 * A331378 A331384 A297150

Adjacent sequences:  A292002 A292003 A292004 * A292006 A292007 A292008

KEYWORD

nonn

AUTHOR

Altug Alkan, Sep 07 2017

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 20 12:58 EST 2020. Contains 332076 sequences. (Running on oeis4.)