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 A287959 Odd primes p such that p^2 divides A001205(p)-(p-1)/2. 0
 3, 43, 8237, 14533, 26153, 11314271 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Carlitz proved that A001205(p) == (p-1)/2 (mod p) for all odd primes p. This sequence consists of odd primes for which A001205(p) == (p-1)/2 (mod p^2) holds. a(7) > 2.3*10^7. - Giovanni Resta, Jun 04 2017 LINKS Leonard Carlitz, Congruences for the Number of n-Gons Formed by n Lines, The American Mathematical Monthly, Vol. 61, No. 6 (1954), pp. 407-411. MATHEMATICA a = 0; a = 0; a = 1; a[n_] := a[n] = (n - 1)*(a[n - 1] + (n - 2)*a[n - 3]/2); lst = {}; k = 3; While[Length[lst] < 5, If[PrimeQ[k] && Divisible[a[k] - (k - 1)/2, k^2], lst = AppendTo[lst, k]]; k++]; lst CROSSREFS Cf. A001205. Sequence in context: A290777 A309401 A190637 * A326970 A076361 A130408 Adjacent sequences:  A287956 A287957 A287958 * A287960 A287961 A287962 KEYWORD nonn,more AUTHOR Amiram Eldar, Jun 03 2017 EXTENSIONS a(6) from Giovanni Resta, Jun 04 2017 STATUS approved

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Last modified June 20 09:57 EDT 2021. Contains 345162 sequences. (Running on oeis4.)