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 A240748 Numbers n such that n^k - (n-1)^k - ... - 3^k - 2^k - 1 is prime for some k. 1
 2, 4, 5, 6, 10, 13 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(7) > 13. See A240747 for more information. a(n) is also the n-values such that A240747(n) is nonzero. It is known that a(n) == 1 mod 4 or 2 mod 4 (except a(2) = 4). If n is not squarefree, then n is not a member of this sequence. It is known that 17, 22, 30, 41, 66, and 194 are members of this sequence. LINKS EXAMPLE There are primes of the form 2^k-1 (A000043) so 2 is a member of this sequence. PROG (PARI) s(n) = for(k=1, 6000, if(ispseudoprime(n^k-sum(i=1, n-1, i^k)), return(k))) n=1; while(n<200, if(s(n), print(n)); n+=1) CROSSREFS Cf. A000043, A240747, A240507, A240503. Sequence in context: A127092 A128171 A233768 * A171165 A039036 A219046 Adjacent sequences:  A240745 A240746 A240747 * A240749 A240750 A240751 KEYWORD nonn,more,hard AUTHOR Derek Orr, Apr 11 2014 STATUS approved

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Last modified June 19 04:44 EDT 2019. Contains 324217 sequences. (Running on oeis4.)