A241473 - OEIS

A241473

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

2, 4, 9, 6, 26, 10, 15, 12, 6543, 52, 74, 18, 76, 56, 36, 24, 289, 27888, 43, 104, 42, 30, 63449, 46, 49, 6398, 115, 51, 2561, 72, 27262, 445685, 118, 48517846, 2246, 78, 268

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OFFSET

1,1

COMMENTS

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

a(38) > 10^8 if it exists. - Michel Marcus, Sep 18 2017

a(38) > 10^12, if it exists. - Giovanni Resta, Aug 19 2019

LINKS

Table of n, a(n) for n=1..37.

EXAMPLE

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

MATHEMATICA

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

PROG

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

CROSSREFS

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

Sequence in context: A011182 A304753 A063507 * A055858 A141389 A348059

Adjacent sequences: A241470 A241471 A241472 * A241474 A241475 A241476

KEYWORD

nonn,base,more,hard

AUTHOR

Michel Lagneau, Apr 23 2014

EXTENSIONS

Data section truncated at index 38 by Michel Marcus, Sep 18 2017

STATUS

approved