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%I #20 Jul 13 2021 13:42:22
%S 1,2,7,2,3,7,5,6,25,3,9,7,11,6,8,14,15,26,17,4,7,10,21,8,23,11,79,6,
%T 27,8,29,30,9,15,5,26,35,18,25,8,39,7,41,10,25,22,45,16,47,23,16,12,
%U 51,79,9,6,17,27,57,8,59,30,26,62,13,43,65,15,44,14,69,54,71,35,25,18,20,26,77,14,241
%N Smallest k such that n divides k*(k+1)*(k+2)/6.
%C More generally we can ask for the smallest k such that gcd(n,f(k)) = n. This sequence has f(k) = k*(k+1)*(k+2)/6. For other examples in the OEIS, see the crossrefencess.
%H David A. Corneth, <a href="/A265647/b265647.txt">Table of n, a(n) for n = 1..10000</a>
%t Table[k = 1; While[! Divisible[k (k + 1) (k + 2)/6, n], k++]; k, {n, 81}] (* _Michael De Vlieger_, Dec 11 2015 *)
%o (PARI) a(n)=my(k=1);while((k*(k+1)*(k+2)/6)%n>0,k++);k \\ _Anders Hellström_, Dec 11 2015
%o (PARI) first(n) = { my(todo = n, i = 1, res = vector(n)); while(todo > 0, d = select(x -> x <= n, divisors(binomial(i + 2, 3))); for(j = 1, #d, if(res[d[j]] == 0, res[d[j]] = i; todo-- ) ); i++ ); res } \\ _David A. Corneth_, Mar 22 2021
%Y Cf. A000292, A011772, A002034, A047930, A005179, A070982, A038700, A344005, A345989.
%K nonn
%O 1,2
%A _Ctibor O. Zizka_, Dec 11 2015
%E More terms from _Michael De Vlieger_, Dec 11 2015
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