OFFSET
1,1
COMMENTS
All the terms are even.
Includes all the numbers of the form p+1 where p is an odd prime (A008864 \ {3}).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
D. R. Heath-Brown, Cheryl E. Praeger and Aner Shalev, Permutation groups, simple groups, and sieve methods, Isr. J. Math., Vol. 148 (2005), pp. 347-375; alternative link.
FORMULA
The number of terms that do not exceed x is N(x) = h * x/log(x) + O(x/log(x)^2), where h = A370746.
MATHEMATICA
q[n_] := AnyTrue[Divisors[n], PrimeQ[n/# - 1] && Divisible[n/# - 2, 2*#] &]; Select[Range[250], q]
PROG
(PARI) is(n) = {my(d = divisors(n)); for(i=1, #d, if(isprime(n/d[i]-1) && !((n/d[i]-2) % (2*d[i])), return(1))); 0; }
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Amiram Eldar, Feb 29 2024
STATUS
approved