A343676 Number of n-digit undulating alternating primes.

4, 9, 23, 49, 175, 321, 1189, 3025, 12111, 28492, 113409, 251513, 1068440, 2629980, 11690210, 28498852, 128871588, 298890814, 1309837146

Offset

1,1

Comments

a(n) is the number of n-digit terms in A343590.

a(n) <= A057333(n).

Links

Table of n, a(n) for n=1..19.

Prog

(Python)
def f(w):
    for s in w:
        for t in range(int(s[-1])+1, 10, 2):
            yield s+str(t)
def g(w):
    for s in w:
        for t in range(1-int(s[-1])%2, int(s[-1]), 2):
            yield s+str(t)
def A343676(n):
    c = 0
    for d in '123456789':
        x = d
        for i in range(1, n):
            x = g(x) if i % 2 else f(x)
        c += sum(1 for p in x if isprime(int(p)))
        if n > 1:
            y = d
            for i in range(1, n):
                y = f(y) if i % 2 else g(y)
            c += sum(1 for p in y if isprime(int(p)))
    return c

Crossrefs

Cf. A002385, A030144, A057333, A059168, A343590, A343675.

Sequence in context: A361002 A138990 A014543 * A131607 A221313 A238832

Adjacent sequences: A343673 A343674 A343675 * A343677 A343678 A343679

Keyword

nonn,base,more

Author

Chai Wah Wu, Apr 25 2021

Extensions

a(18)-a(19) from Martin Ehrenstein, Apr 27 2021

Status

approved