171197

Appears in sequences

• Pentagonal numbers with only odd digits.at n=20A117985
• a(n) = (A002703(n)+2)/2.at n=21A262569
• Composite numbers whose sum of unitary divisors is a multiple of the sum of their aliquot parts.at n=5A273813
• a(n) = a(n-1) + a(n-2) - n*a(floor(n/2)), where a(0) = 1, a(1) = 2, a(2) = 3.at n=22A298401
• Odd numbers k, not powers of primes, such that sigma(k) == 2 modulo 8 and sigma(sigma(k)) == 6 modulo 8.at n=29A332458