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 A342013 Position of the n-th colossally abundant number in A329886, the primorial inflation of Doudna-tree. 5
 1, 2, 5, 9, 19, 21, 37, 75, 139, 267, 535, 539, 555, 1067, 2091, 4139, 8279, 16471, 32855, 32919, 32923, 65691, 131227, 262299, 524599, 1048887, 2097463, 4194615, 4194647, 8388951, 16777559, 33554775, 67109207, 67109463, 134218327, 268436655, 536872111, 536872119, 1073743031, 2147484855, 2147485879, 4294969527, 8589936823 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is the unique integer k such that A329886(k) = A004490(n). Like A342012, also this sequence is monotonic. Proof: the doubling step corresponds here to step *2 + 1, and "bumping up" some of the prime factors likewise results a larger A156552-code, thus both steps keep the result growing. The binary length of these numbers (A070939, = 1+A000523) grows by 0 or 1 at each step, thus the next colossally abundant number is always found on either on the same row (right of the current CA-number), or the next row of A329886, the row immediately below. The next CA-number will be on the same row only when its factorization contains neither a new prime nor yet another instance of prime 2. LINKS Table of n, a(n) for n=1..43. Index entries for sequences computed from indices in prime factorization Index entries for sequences related to sigma(n) FORMULA a(n) = A156552(A342012(n)) = A156552(A319626(A004490(n))). PROG (PARI) 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}; A342013(n) = A156552(A342012(n)); \\ Uses also code from A342012. CROSSREFS Cf. A004490, A005940, A073751, A108951, A156552, A319626, A329886, A329900, A342000, A342010 (the binary weight), A342011, A342012. Sequence in context: A293329 A152546 A286713 * A213544 A265482 A085410 Adjacent sequences: A342010 A342011 A342012 * A342014 A342015 A342016 KEYWORD nonn AUTHOR Antti Karttunen and Michael De Vlieger, Mar 08 2021 STATUS approved

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Last modified June 23 08:04 EDT 2024. Contains 373629 sequences. (Running on oeis4.)