A392497 a(n) is the smallest p-rigid number where p = prime(n).

20, 45, 175, 1001, 1573, 4199, 5491, 12673, 20677, 26071, 47027, 65231, 72283, 107113, 146969, 190747, 212341, 290177, 347261, 367993, 478661, 583573, 716539, 871933, 1009091, 1050703, 1201289, 1247941, 1564259, 1879981, 2279269, 2494633, 2608891, 3127361, 3352351

Offset

1,1

Comments

For the definition of a p-rigid number see A392499.

Links

Table of n, a(n) for n=1..35.

Peter Luschny, Composable, rigid, and sparse numbers. A Python notebook.

Prog

(Python) # Function 'is_rigid' is defined in A392499 (see also links).
from sympy import isprime as is_prime
def first_p_rigid(p: int, limit: int = 10**12) -> int | None:
    if not is_prime(p): return None
    step = p if p == 2 else 2 * p
    for n in range(p*p, limit + 1, step):
        if p != is_rigid(n): continue
        return n
    return None
def A392497_list(upto: int) -> list[int]:
    return [c for n in range(2, upto) if (c := first_p_rigid(n)) is not None]
print(A392497_list(150))

Crossrefs

Cf. A392499, A392496 (p=2), A392495 (p=3).

Sequence in context: A044097 A044478 A228319 * A236474 A145220 A234266

Adjacent sequences: A392494 A392495 A392496 * A392498 A392499 A392500

Keyword

nonn

Author

Peter Luschny, Jan 16 2026

Status

approved