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%I #23 Feb 17 2023 22:13:46
%S 5,10,4,12,2,7,3,28,26,37,13,33,16,6,55,47,64,22,8,25,9,68,91,31,75,
%T 11,34,89,118,96,14,15,136,110,49,117,52,18,163,172,58,138,20,190,67,
%U 159,23,70,24,217,226,180,79,27,244,194,253,85,88,215,280,94,222,298,236,243
%N Another test for divisibility by the n-th prime (see Comments for precise definition).
%C Given a number M, delete its last digit d, then add d*a(n). If the result is divisible by prime(n), then M is also divisible by prime(n). This process may be repeated.
%C a(n) can be quickly calculated by finding the smallest multiple of prime(n) ending in 9, adding one, and dividing that result by 10. E.g., 7 -> 49 -> 5, 11 -> 99 -> 10, 13 -> 39 -> 4, 17 -> 119 -> 12, 19 -> 19 -> 2.
%F a(n) = prime(n) - A103876(n).
%F a(n) = (A114013(n) + 1)/10. - _Hugo Pfoertner_, Jan 28 2023
%o (Python)
%o import sympy
%o [pow(10, -1, p) for p in sympy.primerange(7,348)]
%Y Cf. A103876, A078606, A114013.
%K nonn,base
%O 4,1
%A _Nicholas Stefan Georgescu_, Jan 18 2023
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