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A374665
a(n) is the first number that is the concatenation of n primes and also the product of n primes (counted with multiplicity).
1
2, 22, 222, 2223, 22232, 222222, 2222325, 22222272, 222225552, 2222223255, 22222335232, 222222327525, 2222222372352, 22222222575552, 222222223327232, 2222222225252352, 22222222223327232, 222222222272535552, 2222222222225252352, 22222222222327775232, 222222222222737375232
OFFSET
1,1
COMMENTS
Is this a subsequence of A046034?
FORMULA
A001222(a(n)) = n.
EXAMPLE
a(5) = 22232 because 22232 is the concatenation of the 5 primes 2, 2, 2, 3, 2 and 22232 = 2^3 * 7 * 397 is the product of 5 primes (counted with multiplicity).
MAPLE
f:= proc(n) local k, x, W, L, i;
W:= [2, 3, 5, 7];
for k from 0 to 4^n-1 do
L:= convert(4^n+k, base, 4);
x:= add(W[L[i]+1]*10^(i-1), i=1..n);
if numtheory:-bigomega(x) = n then return x fi;
od;
end proc:
map(f, [$1..20]);
CROSSREFS
Cf. A001222, A046034. Main diagonal of A374376.
Sequence in context: A174200 A137109 A002276 * A112893 A086855 A089182
KEYWORD
nonn,base
AUTHOR
Robert Israel, Jul 15 2024
STATUS
approved