OFFSET
1,2
COMMENTS
See A176558(n) = reverse concatenation of divisors of n. See A175355 for corresponding values of reverse concatenations. Complement of A175354(n) for n >= 2. - Jaroslav Krizek, Apr 20 2010
If prime p divides n, then the exponent of p in the prime factorization of n is odd if p == 1 (mod 3) and even if p == 2 (mod 3). In particular, the sequence has no terms == 2 (mod 3). - Robert Israel, Apr 21 2020
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
4 is a term as 421 is prime; 39 is a term as concatenation of 39,13,3 and 1, i.e. 391331, is prime.
25 is a member as 2551 is prime.
Divisors of 39 are 1,3,13,39; reverse concatenation of divisors 391331 is prime.
48 is a member as 48241612864321 is a prime.
MAPLE
select(n->isprime(parse(cat("", op(sort([op(numtheory[divisors](n))], `>`))))), [$1..3000])[]; (Alec Mihailovs, Aug 14 2005)
MATHEMATICA
Join[{1}, Select[Range[1000], PrimeQ[FromDigits[Flatten[IntegerDigits/@Reverse[Divisors[ #]]]]]&]] (* Harvey P. Dale, Feb 11 2024 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Nov 08 2003
EXTENSIONS
Corrected and extended by David Wasserman, Sep 15 2005
Edited by N. J. A. Sloane, Apr 29 2007, Aug 14 2010
STATUS
approved