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 A239474 Smallest k >= 1 such that k^n-n is prime. a(n) = 0 if no such k exists. 1
 3, 2, 2, 0, 4, 5, 60, 3, 2, 21, 28, 5, 2, 199, 28, 0, 234, 11, 2, 3, 2, 159, 10, 31, 68, 145, 0, 69, 186, 163, 32, 253, 26, 261, 4, 0, 8, 11, 62, 3, 22, 43, 6, 7, 8, 945, 76, 7, 116, 129, 382, 93, 330, 361, 2, 555, 224, 1359, 78, 29, 62, 39, 110, 0, 1032, 37, 462, 29 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If n is of the form (pk)^p for some k and some prime p, then a(n) = 0 (See A097764). LINKS FORMULA a(A097764(n)) = 0 for all n. EXAMPLE 1^1-1 = 0 is not prime. 2^1-1 = 1 is not prime. 3^1-1 = 2 is prime. Thus, a(1) = 3. PROG (Python) import sympy from sympy import isprime def TwoMin(x): ..for k in range(1, 5000): ....if isprime(k**x-x): ......return k x = 1 while x < 100: ..print(TwoMin(x)) ..x += 1 CROSSREFS Cf. A072883, A028870, A153974, A239413, A239414, A239415, A239416, A239417, A239418. Sequence in context: A178609 A144948 A108335 * A326152 A308181 A323557 Adjacent sequences:  A239471 A239472 A239473 * A239475 A239476 A239477 KEYWORD nonn AUTHOR Derek Orr, Mar 20 2014 STATUS approved

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Last modified October 15 21:17 EDT 2019. Contains 328038 sequences. (Running on oeis4.)