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 A347381 a(n) = A252464(n) - A347380(n), where A347380(n) is the length of the common prefix in binary expansions of A156552(n) and A332221(n) = A156552(sigma(n)). 16
 0, 0, 1, 1, 1, 0, 3, 2, 2, 3, 3, 2, 2, 3, 1, 3, 6, 3, 5, 1, 4, 5, 7, 2, 3, 4, 3, 0, 8, 4, 10, 4, 4, 7, 2, 4, 4, 7, 3, 4, 10, 4, 9, 4, 3, 9, 13, 4, 4, 4, 7, 7, 15, 4, 5, 5, 6, 9, 15, 4, 7, 10, 3, 5, 4, 6, 12, 6, 8, 5, 19, 5, 9, 6, 4, 8, 3, 5, 19, 4, 3, 11, 20, 4, 7, 11, 9, 6, 22, 4, 4, 8, 11, 15, 7, 5, 24, 5, 3, 5, 20 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,7 COMMENTS a(n) tells about the degree of relatedness between n and sigma(n) in Doudna tree (see the illustration in A005940). It is 0 for those n where sigma(n) is one of the descendants of n, 1 for those n where the nearest common ancestor of n and sigma(n) is the parent of n, 2 for those n where the nearest common ancestor of n and sigma(n) is the grandparent of n, and so on. LINKS Antti Karttunen, Table of n, a(n) for n = 1..16384 Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537 Index entries for sequences computed from indices in prime factorization Index entries for sequences related to sigma(n) FORMULA a(n) = A252464(n) - A347380(n). PROG (PARI) A000523(n) = logint(n, 2); Abincompreflen(x, y) = if(!x || !y, 0, my(xl=A000523(x), yl=A000523(y), s=min(xl, yl), k=0); x >>= (xl-s); y >>= (yl-s); while(s>=0 && !bitand(1, bitxor(x>>s, y>>s)), s--; k++); (k)); A156552(n) = {my(f = factor(n), p, p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552 A061395(n) = if(n>1, primepi(vecmax(factor(n)[, 1])), 0); A252464(n) = if(1==n, 0, (bigomega(n) + A061395(n) - 1)); A347381(n) = (A252464(n)-Abincompreflen(A156552(n), A156552(sigma(n)))); (PARI) A064989(n) = {my(f); f = factor(n); if((n>1 && f[1, 1]==2), f[1, 2] = 0); for (i=1, #f~, f[i, 1] = precprime(f[i, 1]-1)); factorback(f)}; A252463(n) = if(!(n%2), n/2, A064989(n)); A347381(n) = if(1==n, 0, my(lista=List([]), i, k=n, stemvec, stemlen, sbr=sigma(n)); while(k>1, listput(lista, k); k = A252463(k)); stemvec = Vecrev(Vec(lista)); stemlen = #stemvec; while(1, if((i=vecsearch(stemvec, sbr))>0, return(stemlen-i)); sbr = A252463(sbr))); CROSSREFS Positions of 0 .. 4 in this sequence are given by {2} U A336702, A347391, A347392, A347393, A347394. Cf. A000203, A027687, A156552, A252463, A252464, A332221, A347380, A347383, A347384, A347390. Cf. also A336834. Sequence in context: A125504 A243929 A350285 * A075392 A069901 A115039 Adjacent sequences: A347378 A347379 A347380 * A347382 A347383 A347384 KEYWORD nonn,look AUTHOR Antti Karttunen, Aug 30 2021 STATUS approved

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Last modified December 10 12:10 EST 2023. Contains 367710 sequences. (Running on oeis4.)