primality test please?

[Don Reble]

> A078154
> please check whether the following numbers are really prime

    They're all prime. BTW, since N-1 factors so easily, one can do
    an N-1 proof. PARI does that.

> The corresponding values of n (for n!, strip trailing zeros, and add
> 1) are 1, 2, 3, 5, 6, 14, 15, 24, 74, 191, 222, 276.

    That's A078203.
    The next term is 2200. For those who wish to double-check my N-1
    proof: base-2 works for all N-1 factors but two of them; use base-3
    for 641, and base-5 for 2.

%I A078203
%S A078203 1,2,3,5,6,14,15,24,74,191,222,276,2200
%N A078203 Numbers n such that A004154(n) + 1 is prime.
%t A078203 f[n_] := n!/10^Sum[ Floor[n/5^k], {k, 1, Log[10, n] + 1}]; Do[ If[ PrimeQ[ f[n] + 1], Print[n]], {n, 1, 850}]
%Y A078203 Cf. A004154, A078154, A078190, A078305.
%K A078203 nonn,base
%O A078203 1,2
%A A078203 Cino Hilliard (hillcino368(AT)hotmail.com), Dec 23 2002
%E A078203 Extended by Robert G. Wilson v (rgwv(AT)rgwv.com) and Jason Earls (jcearls(AT)cableone.net), Dec 24 2002
%E A078203 "2200" from Don Reble (djr(AT)nk.ca), Jan 12 2006


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Don Reble  djr at nk.ca  Does njas still my put signatures into the OEIS?

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