A127827 Smallest n-digit emirp (A006567) with nondecreasing digits.
13, 113, 1223, 11149, 111119, 1111339, 11111117, 111111199, 1111111999, 11111111113, 111111111149, 1111111111267, 11111111111257, 111111111113447, 1111111111112227, 11111111111122223, 111111111111113569, 1111111111111113779, 11111111111111133677, 111111111111111111157, 1111111111111111122359, 11111111111111111133469
Offset: 2
Links
- Michael S. Branicky, Table of n, a(n) for n = 2..529 (terms 2..225 from Robert Israel)
Programs
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Maple
nextl:= proc(L) local m,k,r; # L a list of digits 1-9, last odd, in nondecreasing order if L[-1]<= 7 then return subsop(-1=L[-1]+2, L) fi; m:= nops(L); k:= m-1; while L[k] =9 do k:= k-1 od: r:= [op(L[1..k-1]),(L[k]+1) $ (m+1-k)]; if r[-1]::even then r:= subsop(-1=r[-1]+1, r) fi; r end proc: f:= proc(n) local L,p,q,i; L:= [1$n]; do p:= add(L[i]*10^(i-1),i=1..n); q:= add(L[-i]*10^(i-1),i=1..n); if q <> p and isprime(p) and isprime(q) then return(q) fi; L:= nextl(L); od end proc: map(f, [$2..30]); # Robert Israel, Nov 19 2017 -
Python
from sympy import isprime from itertools import count, islice, combinations_with_replacement as mc def bgen(d): nd = ("".join(m) for m in mc("123456789", d)) yield from filter(isprime, map(int, nd)) def ok(ndp): s = str(ndp) return len(set(s)) != 1 and isprime(int(s[::-1])) def agen(): yield from (next(filter(ok, bgen(d))) for d in count(2)) print(list(islice(agen(), 22))) # Michael S. Branicky, Jun 26 2022
Extensions
More terms from Robert Israel, Nov 19 2017