Amiram Eldar, <a href="/A366242/b366242_1.txt">Table of n, a(n) for n = 1..10000</a>

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Every integer k has a unique representation as a product of 2 numbers: one is in this sequence and the other is in A366243: k = A366244(k) * A366245(k).

Amiram Eldar, <a href="/A366242/b366242_1.txt">Table of n, a(n) for n = 1..10000</a>

allocated for Amiram EldarNumbers that are products of "Fermi-Dirac primes" (A050376) that are powers of primes with exponents that are powers of 4.

1, 2, 3, 5, 6, 7, 10, 11, 13, 14, 15, 16, 17, 19, 21, 22, 23, 26, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 41, 42, 43, 46, 47, 48, 51, 53, 55, 57, 58, 59, 61, 62, 65, 66, 67, 69, 70, 71, 73, 74, 77, 78, 79, 80, 81, 82, 83, 85, 86, 87, 89, 91, 93, 94, 95, 96, 97

1,2

A subsequence of A252895, and first differs from it at n = 172. A252895(172) = 256 = 2^(2^3) is not a term of this sequence.

Equivalently, numbers that are products of "Fermi-Dirac primes" that are powers of primes with exponents that are powers of 2 with even exponents.

Products of distinct numbers of the form p^(2^(2*k)), where p is prime and k >= 0.

Numbers whose prime factorization has exponents that are positive terms of the Moser-de Bruijn sequence (A000695).

Every integer k has a unique representation as a product of 2 numbers: one in this sequence and the other in A366243: k = A366244(k) * A366245(k).

The asymptotic density of this sequence is 1/c = 0.65531174251481086750..., where c is given in the formula section.

a(n) ~ c * n, where c = Product_{k>=0} zeta(2^(2*k+1))/zeta(2^(2*k+2)) = 1.52599127273749217982... .

mdQ[n_] := AllTrue[IntegerDigits[n, 4], # < 2 &]; Select[Range[100], AllTrue[FactorInteger[#][[;; , 2]], mdQ] &]

(PARI) ismd(n) = {my(d = digits(n, 4)); for(i = 1, #d, if(d[i] > 1, return(0))); 1; }

is(n) = {my(e = factor(n)[ , 2]); for(i = 1, #e, if(!ismd(e[i]), return(0))); 1; }

Cf. A000695, A050376, A366243, A366244, A366245.

Subsequence of A252895.

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nonn,easy

Amiram Eldar, Oct 05 2023

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