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 A072344 a(n) = the least natural number k such that k*phi(n) + 1 is prime. 3
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 3, 1, 1, 1, 3, 1, 1, 1, 1, 2, 3, 1, 1, 1, 1, 2, 3, 3, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 2, 2, 1, 3, 2, 3, 1, 3, 1, 1, 1, 1, 1, 3, 1, 3, 2, 1, 1, 3, 3, 1, 2, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,15 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A034693(A000010(n)). - Antti Karttunen, Aug 22 2017 EXAMPLE phi(35) = 24 and the least natural number k such that 24 k + 1 is prime is k = 3; so a(35) = 3. MATHEMATICA f[n_] := Module[{i}, i = 0; While[ ! PrimeQ[i*EulerPhi[n] + 1], i++ ]; i]; Table[f[i], {i, 1, 150}] PROG (PARI) A034693(n) = { my(k=1); while(!isprime(1+(k*n)), k++); k; }; A072344(n) = A034693(eulerphi(n)); \\ Antti Karttunen, Aug 22 2017 CROSSREFS Cf. A000010, A034693, A072917. Sequence in context: A243840 A117898 A212810 * A140500 A156054 A030616 Adjacent sequences:  A072341 A072342 A072343 * A072345 A072346 A072347 KEYWORD nonn AUTHOR Joseph L. Pe, Jul 16 2002 STATUS approved

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Last modified August 17 12:30 EDT 2022. Contains 356189 sequences. (Running on oeis4.)