A383030 Indices of the even terms in the sequence of exponentially odd numbers.

2, 5, 7, 8, 11, 16, 18, 19, 22, 24, 26, 29, 31, 33, 35, 39, 41, 43, 46, 48, 51, 54, 56, 58, 61, 63, 67, 69, 72, 74, 76, 79, 82, 84, 86, 87, 91, 93, 96, 98, 100, 103, 106, 109, 110, 113, 115, 119, 121, 122, 124, 126, 129, 131, 133, 136, 139, 144, 147, 149, 152

Offset

1,1

Comments

The asymptotic density of this sequence is 2/5.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

A383029(a(n)) > 0.

Mathematica

expOddQ[n_] := AllTrue[FactorInteger[n][[;; , 2]], OddQ]; Position[Select[Range[350], expOddQ], _?EvenQ] // Flatten

Prog

(PARI) isexpodd(n) = {my(f = factor(n)); for(i=1, #f~, if(!(f[i, 2] % 2), return (0))); 1; }
list(lim) = {my(c = 0); for(k = 1, lim, if(isexpodd(k), c++; if(!(k % 2), print1(c, ", ")))); }

Crossrefs

Cf. A268335, A376218, A383029, A383031.

Sequence in context: A153308 A370856 A216565 * A285938 A325441 A192111

Adjacent sequences: A383027 A383028 A383029 * A383031 A383032 A383033

Keyword

nonn,easy

Author

Amiram Eldar, Apr 13 2025

Status

approved