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A289337 Composite numbers (pseudoprimes) n, that are not Carmichael numbers, such that A000670(n-1) == 0 (mod n). 1
25, 125, 325, 451, 1561, 4089, 7107, 8625, 12025 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

I. J. Good proved that A000670(k*(p-1)) == 0 (mod p) for all k >= 1 and prime p. Therefore the congruence A000670(n-1) == 0 (mod n) holds for all primes and Carmichael numbers. This sequence consist of the other composite numbers for which the congruence holds.

LINKS

Table of n, a(n) for n=1..9.

I. J. Good, The number of orderings of n candidates when ties are permitted, Fibonacci Quarterly, Vol. 13 (1975), pp. 11-18.

EXAMPLE

A000670(24) = 2958279121074145472650648875 is divisible by 25 and 25 is not a prime, nor a Carmichael number.

MATHEMATICA

a[0] = 1; a[n_] := a[n] = Sum[Binomial[n, k]*a[n - k], {k, 1, n}]; carmichaelQ[n_]:=(Mod[n, CarmichaelLambda[n]] == 1); seqQ[n_] := !carmichaelQ[n] && Divisible[a[n-1], n]; Select[Range[2, 500], seqQ]

CROSSREFS

Cf. A000670, A002997, A289338.

Sequence in context: A044738 A062672 A036321 * A211581 A226231 A211595

Adjacent sequences: A289334 A289335 A289336 * A289338 A289339 A289340

KEYWORD

nonn,more

AUTHOR

Amiram Eldar, Jul 02 2017

STATUS

approved

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Last modified January 31 20:46 EST 2023. Contains 359981 sequences. (Running on oeis4.)