A223458 Primes whose first digit is a composite number.

41, 43, 47, 61, 67, 83, 89, 97, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881

Offset

1,1

Links

K. D. Bajpai, Table of n, a(n) for n = 1..10000

Example

409 is a prime number whose first digit is 4, a composite number, so 409 is a term.

Maple

KD := proc() local a, b, d, e;  a:= ithprime(n);  b:=length(a);  d:=a/(10^(b-1));  e:=floor(d); if isprime(e)=false and e>1 then RETURN (a): fi; end: seq(KD(), n=1..200);

Prog

(Python)
from sympy import primerange
from itertools import count, islice
def agen(): yield from (p for e in count(1) for k in [4, 6, 8, 9] for p in primerange(k*10**e, (k+1)*10**e))
print(list(islice(agen(), 54))) # Michael S. Branicky, Jun 25 2022

Crossrefs

Cf. A069090 (primes none of whose proper initial segments are primes).

Sequence in context: A005846 A273756 A154498 * A243429 A345346 A062669

Adjacent sequences: A223455 A223456 A223457 * A223459 A223460 A223461

Keyword

nonn,base

Author

K. D. Bajpai, Aug 24 2013

Status

approved