A217068 Least number m such that phi(m-6n) = phi(m) = phi(m+6n) and m is not divisible by n.

7991, 4096740829, 651, 25056, 23973, 41526, 1302, 5005333, 8175, 504, 1953, 2919396, 13737, 1054, 2257, 1708, 11521, 22313, 16350, 123098, 1008, 1584, 3906, 1887, 89027, 5335754, 27474, 59550082, 2108, 1344, 4514, 1512, 3416, 2925, 5859, 494379, 44626, 1586993, 8557

Offset: 2

Author

Michel Marcus, Sep 26 2012

Keywords

• nonn

Comments

a(n) has been computed by Donovan Johnson up to 200, but no values were found below 2*10^11 for n=41, 67, 113, 149, 157, 181.

Links

• F. Firoozbakht, Puzzle 466. phi(n-1)=phi(n)=phi(n+1), in C. Rivera's Primepuzzles.
• S. W. Graham, J. J. Holt and C. Pomerance, On the solutions to phi(n) = phi(n+k) Number Theory in Progress, K. Gyory, H. Iwaniec, and J. Urbanowicz, eds., vol. 2, de Gruyter, Berlin and New York, 1999, pp. 867-882.
• Donovan Johnson and Michel Marcus, a(n) for n=2 to 200, with missing terms shown as 0.

Crossrefs

Cf. A000010, A217006.