OFFSET
1,1
COMMENTS
Primes p such that 10^p is divisible by p+1. Primes p whose fractions p/(p+1) are terminating decimals, i.e., primes p such that A158911(p)=0. Primes p such that the prime divisors of p+1 are also prime divisors of the numbers m obtained by the concatenation of p and p+1. For example, for p=19, m = 1920, the prime divisors of 20 are {2, 5} and the prime divisors of 1920 are {2, 3, 5}. - Jaroslav Krizek, Feb 25 2013
For n > 1, all terms are congruent to 1 (mod 6). - Muniru A Asiru, Sep 29 2017
LINKS
Ray Chandler, Table of n, a(n) for n = 1..4222
EXAMPLE
1250000 = 2*2*2*2*5*5*5*5*5*5*5 and 1250000 - 1 = A000040(96469), therefore 1249999 is a term.
List of (r, s): (2, 0), (3, 0), (2, 1), (5, 0), (4, 1), (7, 0), (3, 2), (2, 3), (1, 4), (8, 1), (4, 3), (3, 4), (10, 1), ... - Muniru A Asiru, Sep 29 2017
MATHEMATICA
With[{n = 10^8}, Union@ Select[Flatten@ Table[2^p*5^q - 1, {p, 0, Log[2, n/(1)]}, {q, 0, Log[5, n/(2^p)]}], PrimeQ]] (* Michael De Vlieger, Sep 30 2017 *)
PROG
(GAP)
A:=Filtered([1..10^7], IsPrime);; I:=[5];;
B:=List(A, i->Elements(Factors(i+1)));;
C:=List([0..Length(I)], j->List(Combinations(I, j), i->Concatenation([2], i)));;
A077313:=List(Set(Flat(List([1..Length(C)], i->List([1..Length(C[i])], j->Positions(B, C[i][j]))))), i->A[i]); # Muniru A Asiru, Sep 29 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Nov 04 2002
EXTENSIONS
More terms from Reinhard Zumkeller, Nov 15 2002
More terms from Vladeta Jovovic, May 08 2003
STATUS
approved