A218466 Least k > n for which phi(k - n) = phi(k + n) or 0 if no such k exists.

5, 10, 27, 17, 25, 54, 23, 34, 61, 47, 55, 108, 47, 46, 139, 68, 58, 122, 71, 85, 144, 95, 115, 207, 101, 94, 183, 92, 145, 278, 104, 136, 177, 116, 175, 244, 161, 142, 306, 149, 184, 283, 191, 187, 410, 230, 235, 267, 146, 202, 299, 188, 157, 366, 275, 184

Offset: 1

Author

Irina Gerasimova, Mar 26 2013

Keywords

• nonn

Comments

Is there an upper bound for a(n) for a given n? - Michael B. Porter, Apr 06 2013

Examples

			a(3) = 27 since phi(27 - 3) = phi(24) = 8 and phi(27 + 3) = phi(30) = 8, and 27 is the smallest number greater than 3 for which the two are equal.
		

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010, A217768, A223091.

Programs

PARI

/* will not terminate if k does not exist */
a218446(n) = {local(k); k = n + 1; while(eulerphi(k - n) <> eulerphi(k + n), k = k + 1); k} \\ Michael B. Porter, Mar 30 2013

Extensions

Extended by R. J. Mathar, Mar 27 2013