OFFSET
1,2
COMMENTS
The numbers of terms not exceeding 10^k, for k = 1, 2, ..., are 6, 48, 478, 4734, 47195, 471707, 4716892, 47168363, 471681183, 4716806520, ... . Apparently, the asymptotic density of this sequence exists and equals Product_{p prime} (1 - 2/(p*(p+1))) = 0.47168... (A307868).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
expOddQ[n_] := AllTrue[FactorInteger[n][[;; , 2]], OddQ]; Select[Range[128], And @@ expOddQ /@ {#, # + 1} &]
PROG
(PARI) isexpodd(n) = {my(f = factor(n)); for(i=1, #f~, if (!(f[i, 2] % 2), return (0))); 1; }
is(n) = isexpodd(n) && isexpodd(n+1)
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 27 2023
STATUS
approved