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0,4

The sequence of indices of odd terms b(n) begins: 7, 9, 25, 27, 39, 43, 45, 49, 53, 57, 59, 65, 67, 71, ...

a(n) may be odd only if n is odd. For even n's, both (n+2)^(n+2) and n^n are even, therefore a(n) is even.

c(n) = (b(n)-1)/2 begins: 3, 4, 12, 13, 19, 21, 22, 24, 26, 28, 29, 32, 33, 35, 36, 37, 38, 41, ...

Table of n, a(n) for n=0..20.

a(3) = 5^5 mod 3^3 = 3125 mod 27 = 20.

(Python)

for i in range(21): print str((i+2)**(i+2) % (i**i))+', ',

Cf. A066611, A176823, A176824.

Sequence in context: A187156 A246877 A074632 * A228839 A158444 A235281

Adjacent sequences: A225187 A225188 A225189 * A225191 A225192 A225193

nonn,less

Alex Ratushnyak, May 01 2013

approved