A253721 Triprimes modulo 10.

8, 2, 8, 0, 7, 8, 0, 2, 4, 5, 0, 2, 3, 6, 8, 0, 5, 6, 8, 2, 8, 9, 2, 5, 0, 4, 6, 7, 4, 5, 0, 8, 7, 8, 3, 4, 4, 5, 0, 1, 2, 4, 5, 2, 6, 8, 0, 5, 7, 2, 2, 0, 1, 6, 8, 2, 4, 5, 6, 5, 8, 1, 6, 8, 3, 5, 9, 2, 4, 5, 6, 0, 2, 0, 6, 8, 2, 5, 2, 3, 8, 3, 5, 4, 6, 7

Offset

1,1

Comments

Last digit of triprimes (A014612).

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Index entries for sequences related to final digits of numbers

Formula

a(n) = A010879(A014612(n)). - Michel Marcus, May 03 2015

Maple

with(numtheory): A253721:=n->`if`(bigomega(n) = 3, n mod 10, NULL): seq(A253721(n), n=1..500);

Mathematica

Mod[#, 10] & /@ Select[Range[500], PrimeOmega[#] == 3 &]

Prog

(Haskell)
a253721 = flip mod 10 . a014612  -- Reinhard Zumkeller, May 05 2015
(PARI) do(x)=my(v=List(), t); forprime(p=2, x\4, forprime(q=2, min(x\(2*p), p), t=p*q; forprime(r=2, min(x\t, q), listput(v, t*r)))); Set(v)%10 \\ Charles R Greathouse IV, Aug 30 2017
(Python)
from math import isqrt
from sympy import primepi, primerange, integer_nthroot
def A253721(n):
    def f(x): return int(n+x-sum(primepi(x//(k*m))-b for a, k in enumerate(primerange(integer_nthroot(x, 3)[0]+1)) for b, m in enumerate(primerange(k, isqrt(x//k)+1), a)))
    m, k = n, f(n)
    while m != k:
        m, k = k, f(k)
    return m%10 # Chai Wah Wu, Aug 17 2024

Crossrefs

Cf. A010879 (final digit of n), A014612 (triprimes).

Cf. A007652 (primes mod 10), A106146 (semiprimes mod 10).

Cf. A255646 (subsequence).

Sequence in context: A134724 A269546 A248299 * A021551 A143025 A303326

Adjacent sequences: A253718 A253719 A253720 * A253722 A253723 A253724

Keyword

nonn,base,easy

Author

Wesley Ivan Hurt, May 02 2015

Status

approved