A246447 The odd primes squared plus 1 and the composites squared minus 1.

10, 15, 26, 35, 50, 63, 80, 99, 122, 143, 170, 195, 224, 255, 290, 323, 362, 399, 440, 483, 530, 575, 624, 675, 728, 783, 842, 899, 962, 1023, 1088, 1155, 1224, 1295, 1370, 1443, 1520, 1599, 1682, 1763, 1850, 1935, 2024, 2115, 2210, 2303, 2400, 2499, 2600

Offset

1,1

Comments

The odd primes squared plus 1 and the nonprimes squared minus 1 are the numerators or denominators of an infinite product converging to 1 whose denominators or numerators, conversely, are the squares of said numbers, that is, (p^2+1/p^2)*(q^2-1)/q^2)..., where p is an odd prime and q is a nonprime.

Union of A066872 and (A062312 - 1) with 0 and 5 removed. - Robert Israel, Aug 26 2014

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Prog

(PARI) lista(nn) = {for (n=3, nn, if (isprime(n), print1(n^2+1, ", "), print1(n^2-1, ", ")); ); } \\ Michel Marcus, Aug 26 2014
(Python)
for n in range(3, 10**3):
..if isprime(n):
....print(n**2+1, end=', ')
..else:
....print(n**2-1, end=', ') # Derek Orr, Sep 19 2014

Crossrefs

Cf. A066872, A062312.

Sequence in context: A029702 A053330 A051990 * A254362 A182427 A171956

Adjacent sequences: A246444 A246445 A246446 * A246448 A246449 A246450

Keyword

nonn,easy

Author

Leo Depuydt, Aug 26 2014

Extensions

More terms from Michel Marcus, Aug 26 2014

Status

approved