cp's OEIS Frontend

A345056 a(n) is the next larger number k > n for which A011772(k) = A011772(n), or n itself if no such larger number exists.

%I A345056 #11 Jun 07 2021 21:03:31
%S A345056 1,6,3,14,10,6,21,20,12,10,55,18,26,28,15,62,34,36,57,24,21,33,253,30,
%T A345056 50,39,117,28,58,40,93,72,66,68,105,36,74,95,78,60,82,70,129,48,45,69,
%U A345056 1081,88,56,75,153,130,106,63,55,84,171,203,1711,120,122,124,126,254,325,66,201,136,92,210,355,96,146,111,100,114
%N A345056 a(n) is the next larger number k > n for which A011772(k) = A011772(n), or n itself if no such larger number exists.
%F A345056 a(n) = n + A345057(n).
%o A345056 (PARI)
%o A345056 A011772(n) = { if(n==1, return(1)); my(f=factor(if(n%2, n, 2*n)), step=vecmax(vector(#f~, i, f[i, 1]^f[i, 2]))); forstep(m=step, 2*n, step, if(m*(m-1)/2%n==0, return(m-1)); if(m*(m+1)/2%n==0, return(m))); }; \\ From A011772
%o A345056 A345056(n) = { my(x=A011772(n), y=binomial(x+1,2)); for(i=1+n,y,if(A011772(i)==x,return(i))); (n); };
%Y A345056 Cf. A000217, A002024, A011772, A066561, A345057, A345058.
%K A345056 nonn
%O A345056 1,2
%A A345056 _Antti Karttunen_, Jun 07 2021