A217741 Squarefree nonprimes n with a divisor d such that phi(n) divides n+d.

1, 2, 3, 6, 10, 15, 21, 30, 42, 70, 110, 210, 255, 285, 465, 510, 570, 930, 1430, 2530, 2590, 2870, 3010, 4970, 6699, 13398, 27645, 28785, 54435, 55290, 57570, 64790, 65535, 66990, 69105, 78285, 108870, 118910, 131070, 138210, 156570, 224510

Offset

1,2

Comments

There are only 42 such numbers below 3*10^5. - M. F. Hasler, Apr 06 2013

Links

Donovan Johnson, Table of n, a(n) for n = 1..200

Example

For n=70, phi(70)=24 and 2 is a divisor of 70; since 24 | 70+2, the number n=70 is a term of this sequence.

Prog

(PARI) is(n)=issquarefree(n)&&sumdiv(n, d, (n+d)%eulerphi(n)==0) \\ Charles R Greathouse IV, Apr 02 2013
(PARI) is_A217741(n)={ my(p); issquarefree(n) && fordiv(n+!p=eulerphi(n), d, (n+d)%p || return(1))} \\ - M. F. Hasler, Apr 06 2013

Crossrefs

Sequence in context: A356314 A102366 A152452 * A074134 A056178 A320597

Adjacent sequences: A217738 A217739 A217740 * A217742 A217743 A217744

Keyword

nonn

Author

J. M. Bergot, Apr 02 2013

Extensions

Name corrected by Donovan Johnson, Apr 08 2013

Status

approved