A137728 Second digit from the end of product of first n primes.

0, 0, 3, 1, 1, 3, 1, 9, 7, 3, 3, 1, 1, 3, 1, 3, 7, 7, 9, 9, 7, 3, 9, 1, 7, 7, 1, 7, 3, 9, 3, 3, 1, 9, 1, 1, 7, 1, 7, 1, 9, 9, 9, 7, 9, 1, 1, 3, 1, 9, 7, 3, 3, 3, 1, 3, 7, 7, 9, 9, 7, 1, 7, 7, 1, 7, 7, 9, 3, 7, 1, 9, 3, 9, 1, 3, 7, 9, 9, 1, 9, 9, 9, 7, 3, 9, 1, 7, 7, 1, 7, 3, 1, 1, 9, 7, 3, 3, 9, 9, 3, 1, 3, 7, 7

Offset

1,3

Comments

a(1) = a(2) = 0 because prime(1) = 2 and prime(1)*prime(2) = 6 are one-digit numbers.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A002110(n)/10 mod 10 for n > 2; a(1) = a(2) = 0.

Maple

a[1]:= 0: a[2]:= 0: a[3]:= 3: p:= 5:
for n from 4 to 1000 do
  p:= nextprime(p);
  a[n]:= (a[n-1] * p) mod 10:
od: # Robert Israel, Nov 22 2018

Mathematica

a(1) = a(2) = 0, for n>2 Table[ Mod[ Product[ Prime[n], {n, 1, k} ], 100 ]/10, {k, 3, 1000} ]

Crossrefs

Cf. A007652 = Final digit of prime(n).

Cf. A110923 = Final two digits of prime(n).

Cf. A137727 = Final digit of prime(n)*prime(n+1).

Cf. A002110 = Primorial numbers, p#.

Sequence in context: A341050 A122506 A010274 * A054398 A093415 A233508

Adjacent sequences: A137725 A137726 A137727 * A137729 A137730 A137731

Keyword

nonn,base

Author

Alexander Adamchuk, Feb 08 2008

Status

approved