21079

Appears in sequences

• When squared gives number composed just of the digits 1, 2, 3, 4.at n=33A061677
• a(n) = Sum {k + j*m <= n} (k + j*m), with 0 < k,j,m <= n.at n=27A106847
• Composite numbers, not ending with 0, sharing a 3-digit sequence with some of its prime factors.at n=19A131523
• a(1) = 1; thereafter a(n) is always the smallest integer > a(n-1) not leading to a contradiction, such that any five consecutive digits in the sequence sum up to a prime.at n=39A152605
• Positive integers of the form (7*m^2+1)/11.at n=33A179370
• G.f.: exp( Sum_{n>=1} (2^n + (-1)^n)^n * x^n/n ).at n=4A211897
• Number of set partitions of [n] such that all absolute differences between least elements of consecutive blocks are <= six.at n=9A287256
• Numbers k such that (2*10^k - 179)/3 is prime.at n=16A295394
• Numbers k at which point A336459(k) appears multiplicative, but A051027(k) does not.at n=37A336561
• Numbers k such that A353802(k) / sigma(sigma(k)) is an integer > 1, where A353802(n) = Product_{p^e||n} sigma(sigma(p^e)).at n=11A353807
• The positive odd numbers x such that x = c^2 - y and +-x = a +- y, where (a,b,c) is a primitive Pythagorean triple (PPT), a is odd and y is an even positive integer.at n=33A357535
• a(n) = floor(a(n-1)*3/2) with a(1) = 5.at n=21A381677