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a(n) is the smallest k such that phi(k) = reverse(k-n), or 0 if no such k exists.
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%I #23 Aug 19 2019 08:08:42

%S 2,4,9,6,26,10,15,12,6543,52,74,18,76,56,36,24,289,27888,43,104,42,30,

%T 63449,46,49,6398,115,51,2561,72,27262,445685,118,48517846,2246,78,268

%N a(n) is the smallest k such that phi(k) = reverse(k-n), or 0 if no such k exists.

%C phi(n) = A000010(n) is the Euler totient function.

%C a(38) > 10^8 if it exists. - _Michel Marcus_, Sep 18 2017

%C a(38) > 10^12, if it exists. - _Giovanni Resta_, Aug 19 2019

%e a(23) = 63449 because phi(63449) = 62436 = reverse(63426) = reverse(63449-23).

%t Table[k = n+1; While[EulerPhi[k] != FromDigits[ Reverse[ IntegerDigits[k-n] ]], k++]; k, {n, 25}]

%o (PARI) a(n) = {my(k = n+1); while (eulerphi(k) != fromdigits(Vecrev(digits(k-n))), k++); k;} \\ _Michel Marcus_, Sep 18 2017

%Y Cf. A000010, A004086, A230028 (case n=20).

%K nonn,base,more,hard

%O 1,1

%A _Michel Lagneau_, Apr 23 2014

%E Data section truncated at index 38 by _Michel Marcus_, Sep 18 2017