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A028864
Primes with digits in nondecreasing order.
17
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 37, 47, 59, 67, 79, 89, 113, 127, 137, 139, 149, 157, 167, 179, 199, 223, 227, 229, 233, 239, 257, 269, 277, 337, 347, 349, 359, 367, 379, 389, 449, 457, 467, 479, 499, 557, 569, 577, 599, 677, 1117, 1123, 1129
OFFSET
1,1
COMMENTS
Identical digits are acceptable, e.g., 1117 is in the sequence. - Harvey P. Dale, Aug 16 2011
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000 (terms n = 1..1000 from T. D. Noe)
FORMULA
Trivially, a(n) >> exp(n^(1/10)). - Charles R Greathouse IV, Mar 15 2014
prime(n) = A028905(n) if prime(n) is in this sequence. - Alonso del Arte, Nov 25 2019
MATHEMATICA
daoQ[n_] := Count[Differences[IntegerDigits[n]], _?(# < 0 &)] == 0; Select[Prime[Range[200]], daoQ] (* Harvey P. Dale, Aug 16 2011 *)
Select[Prime[Range[200]], Min[Differences[IntegerDigits[#]]]>-1&] (* Harvey P. Dale, Mar 02 2023 *)
PROG
(R) j=2; y=as.bigz(c()); while(j<1000) {
x=sort(as.numeric(strsplit(as.character(j), spl="")[[1]]), decr=F)
if(j==paste(x[x>0], collapse="")) y=c(y, j)
j=nextprime(j)
} // Christian N. K. Anderson, Apr 04 2013
(PARI) select(n->n=digits(n); n==vecsort(n), primes(500)) \\ Charles R Greathouse IV, Mar 15 2014
(Magma) [p:p in PrimesUpTo(1200)| Reverse(Intseq(p)) eq Sort(Intseq(p))]; // Marius A. Burtea, Nov 29 2019
(Python)
from itertools import count, islice, combinations_with_replacement
from sympy import isprime
def A028864_gen(): # generator of terms
yield from (2, 3, 5, 7)
a, b = {'1':0, '2':1, '3':1, '4':2, '5':2, '6':2, '7':2, '8':3, '9':3}, (1, 3, 7, 9)
for l in count(1):
for d in combinations_with_replacement('123456789', l):
k = 10*int(''.join(d))
for e in b[a[d[-1]]:]:
if isprime(m:=k+e):
yield m
A028864_list = list(islice(A028864_gen(), 30)) # Chai Wah Wu, Dec 25 2023
CROSSREFS
KEYWORD
nonn,base,nice
EXTENSIONS
Definition corrected by Omar E. Pol, Mar 22 2012
STATUS
approved